The effect of aging on adrenergic and nonadrenergic receptor expression and responsiveness in canine skeletal muscle

We tested the hypothesis that adrenergic and nonadrenergic receptor responsiveness and protein expression would be altered with advancing age. Young (n = 6; 22 ± 1 mo; mean ± SE) and old (n = 6; 118 ± 9 mo) beagles were instrumented with flow probes and an indwelling catheter for continuous measurement of external iliac blood flow and arterial blood pressure. Vascular conductance (VC) was calculated as hindlimb blood flow/mean arterial pressure. Selective agonists for α-1, α-2, neuropeptide-Y (NPY), and purinergic (P2X) receptors were infused at rest and during treadmill running at moderate (2.5 mph) and heavy (4 mph with 2.5% grade) exercise intensities. Feed arteries were dissected from gracilis muscles, and α-1D, α-1B, α-2A, P2X-4, P2X-1, and NPY-Y1 receptor protein expression was determined. Phenylephrine produced similar decreases (P > 0.05) in VC in young and old beagles at rest (young: -62 ± 5%; old: -59 ± 5%) and during moderate (young: -67 ± 5%; old: -62 ± 4%) and heavy (young: -54 ± 4%; old: -49 ± 3%) exercise. Clonidine caused similar (P > 0.05) decreases in VC in old compared with young dogs at rest (young: -59 ± 8%; old: -70 ± 6%) and during moderate (young: -52 ± 6%; old: -47 ± 5%)- and heavy (young: -42 ± 5%; old: -43 ± 5%)-intensity exercise. NPY infusion resulted in a similar decline in VC in young and old beagles at rest (young: -40 ± 7%; old: -39 ± 9%) and during moderate (young: -47 ± 6%; old: -40 ± 6%)- and heavy (young: -40 ± 3%; old: -38 ± 4%)-intensity exercise. α-β-Methylene-ATP also produced similar decreases in VC in young and old beagles at rest (young: -36 ± 6%; old: -40 ± 8%) and during exercise at moderate (young: -42 ± 5%; old: -40 ± 9%) and heavy (young: -47 ± 5%; old: -42 ± 8%) intensities. α-1B receptor protein expression was elevated (P < 0.05) in old compared with young dogs, whereas there were no age-related differences in α-1D or α-2A receptor expression and nonadrenergic P2X-4, P2X-1, and NPY-Y1 receptor expression. The present findings indicate that postsynaptic adrenergic and nonadrenergic receptor responsiveness was not altered by advancing age. Moreover, the expression of adrenergic and nonadrenergic receptors in skeletal-muscle feed arteries was largely unaffected by aging.

Is tonic sympathetic vasoconstriction increased in the skeletal muscle vasculature of aged canines?

We tested the hypothesis that tonic adrenergic and nonadrenergic receptor-mediated sympathetic vasoconstriction would increase at rest and during exercise with advancing age. Young (n = 6; 22 ± 1 mo; means ± SE) and old (n = 6; 118 ± 9 mo) beagles were studied. Selective antagonists for alpha-1, alpha-2, neuropeptide Y (NPY), and purinergic (P(2x)) receptors were infused at rest and during treadmill running at 2.5 mph and 4 mph with 2.5% grade. Prazosin produced similar increases in vascular conductance in young and old beagles at rest (Young: 158 ± 34%; Old: 98 ± 19%) and during exercise at 2.5 mph (Young: 80 ± 10%; Old: 58 ± 12%) and 4 mph and 2.5% grade (Young: 57 ± 5%; Old: 26 ± 4%). Rauwolscine caused similar (P > 0.05) increases in vascular conductance in old compared with young dogs at rest (Young: 119 ± 25%; Old: 64 ± 22%) and at 2.5 mph (Young: 86 ± 13%; Old: 60 ± 7%) and 4 mph with 2.5% grade (Young: 61 ± 5%; Old: 43 ± 7%). N2-(diphenylacetyl)-N-[4-hydroxyphenyl)methyl]-d-arginine amide (BIBP) caused a smaller increase (P < 0.05) in vascular conductance in old compared with young dogs at rest (Young: 179 ± 44%; Old: 91 ± 22%), whereas similar increases (P > 0.05) of experimental limb vascular conductance in young and old dogs occurred following BIBP during exercise at 2.5 mph (Young: 56 ± 16%; Old: 50 ± 12%) and 4 mph and 2.5% grade (Young: 45 ± 10%; Old: 25 ± 7%). Pyridoxal-phosphate-6-azophenyl-2'-4'-disulfonic acid infusion produced a larger increase in vascular conductance in old compared with young beagles at rest (Young: 88 ± 14%; Old: 191 ± 58%), whereas similar increases were observed at 2.5 mph (Young: 47 ± 18%; Old: 31 ± 11%) and 4 mph with 2.5% grade (Young: 26 ± 13%; Old: -18 ± 8%). At rest, NPY receptor-mediated restraint of skeletal muscle blood flow was reduced with advancing age, whereas P(2x) receptor-mediated restraint of skeletal muscle blood flow was increased. During exercise, the magnitude of adrenergic and nonadrenergic sympathetic vasoconstriction was not different between young and old dogs. Overall, these data demonstrate that adrenergic receptor-mediated vasoconstriction was not elevated at rest, but nonadrenergic sympathetic vasoconstriction was altered under basal conditions in aged beagles.

Absence of flow-mediated vasodilation in the rabbit femoral artery

The purpose of this study was to determine if there is flow-mediated vasodilation of the femoral artery in response to progressive increases in flow within a physiological range observed in the in vivo experiments. Femoral artery blood flow was determined in conscious rabbits (n = 5) using chronically implanted flowprobes. Resting blood flow was 8.3 +/- 0.6 ml/min and increased to 39.9 +/- 5.4 ml/min during high intensity exercise. Femoral arteries (n = 12, 1705 +/- 43 microm outer diameter) harvested from a separate group of rabbits were mounted on cannulas and diameter was continuously monitored by video system. Functional integrity of the endothelium was tested with acetylcholine. The arteries were set at a transmural pressure of 100 mm Hg and preconstricted with phenylephrine to 73 +/- 3% of initial diameter. Using a roller pump with pressure held constant, the arteries were perfused intraluminally with warmed, oxygenated Krebs' solution (pH = 7.4) over a physiological range of flows up to 35 ml/min. As flow increased from 5 ml/min to 35 ml/min, diameter decreased significantly (p < 0.05) from 1285 +/- 58 microm to 1100 +/- 49 microm. Thus, in vessels with a functional endothelium, increasing intraluminal flow over a physiological range of flows produced constriction, not dilation. Based on these results, it seems unlikely that flow-mediated vasodilation in the rabbit femoral artery contributes to exercise hyperemia.

The paradox of sympathetic vasoconstriction in exercising skeletal muscle

Is there sympathetic vasoconstriction in exercising skeletal muscle? Although convincing evidence exists that demonstrates vasoconstriction in active muscle, the proposition that the sympathetic nervous system constricts skeletal muscle during exercise poses a paradox, given the robust vasodilation that occurs in muscle during exercise. Ultimately, muscle perfusion is a balance between metabolic vasodilation and sympathetic vasoconstriction.

Parasympathetic innervation of canine tracheal smooth muscle

To investigate whether efferent parasympathetic fibers to the tracheal smooth muscle course through the pararecurrent nerve rather than the recurrent or the superior laryngeal nerve, we stimulated all three nerves in anesthetized dogs. We also recorded the pararecurrent nerve activity response to bronchoconstrictor stimuli and compared it with pressure changes inside a saline-filled cuff of an endotracheal tube. Electrical stimulation (30 s, 100 Hz, 0.1 ms, 10 mA) increased tracheal cuff pressure by 21.0 +/- 3.2 and 1.3 +/- 0.7 cmH(2)O for the pararecurrent and the recurrent laryngeal nerve, respectively. Stimulation of the superior laryngeal nerve increased tracheal cuff pressure before, but not after, sectioning of the ramus anastomoticus, which connects it to the pararecurrent nerve. Intravenous administration of sodium cyanide increased pararecurrent nerve activity by 208 +/- 51% and tracheal cuff pressure by 14.4 +/- 3.5 cmH(2)O. Elevation of end-tidal PCO(2) to 50 Torr increased pararecurrent nerve activity by 49 +/- 19% and tracheal cuff pressure by 8.4 +/- 3.6 cmH(2)O. Further elevation to 60 Torr increased pararecurrent nerve activity by 101 +/- 33% and tracheal cuff pressure by 11.3 +/- 2.9 cmH(2)O. These results lead us to the conclusion that parasympathetic efferent fibers reach the smooth muscle of the canine trachea via the pararecurrent nerve.

Exercise attenuates alpha-adrenergic-receptor responsiveness in skeletal muscle vasculature

Attenuation of sympathetic vasoconstriction (sympatholysis) in working muscles during dynamic exercise is controversial. A potential mechanism is a reduction in alpha-adrenergic-receptor responsiveness. The purpose of this study was to examine alpha(1)- and alpha(2)-adrenergic-receptor-mediated vasoconstriction in resting and exercising skeletal muscle using intra-arterial infusions of selective agonists. Thirteen mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and a catheter in one femoral artery. The selective alpha(1)-adrenergic agonist (phenylephrine) or the selective alpha(2)-adrenergic agonist (clonidine) was infused as a bolus into the femoral artery catheter at rest and during mild and heavy exercise. Intra-arterial infusions of phenylephrine elicited reductions in vascular conductance of 76 +/- 4, 71 +/- 5, and 31 +/- 2% at rest, 3 miles/h, and 6 miles/h and 10% grade, respectively. Intra-arterial clonidine reduced vascular conductance by 81 +/- 5, 49 +/- 4, and 14 +/- 2%, respectively. The response to intra-arterial infusion of clonidine was unaffected by surgical sympathetic denervation. Agonist infusion did not affect either systemic blood pressure, heart rate, or blood flow in the contralateral iliac artery. alpha(1)-Adrenergic-receptor responsiveness was attenuated during heavy exercise. In contrast, alpha(2)-adrenergic-receptor responsiveness was attenuated even at a mild exercise intensity. These results suggest that the mechanism of exercise sympatholysis may involve reductions in postsynaptic alpha-adrenergic-receptor responsiveness.

Dynamic exercise attenuates sympathetic responsiveness of canine vascular smooth muscle

The phenomenon of reduced responsiveness of the skeletal muscle arterial vasculature to sympathetic activation during exercise (sympatholysis) remains controversial. The purpose of this study was to examine the vascular effects of sympathoactivation in dynamically exercising skeletal muscle. Mongrel dogs (19-24 kg) were instrumented chronically with transit-time ultrasonic flow probes on the external iliac arteries. After pretreatment with atropine (0.2 mg/kg), an intravenous bolus (4 microg/kg) of a nicotinic ganglion stimulant [1,1-dimethyl-4-phenylpiperazinium iodide (DMPP)] was given at rest and during treadmill exercise at graded intensities. Administration of DMPP was associated with prompt reductions in iliac blood flow and increases in arterial pressure under all conditions. There were significant reductions (P < 0.05) in iliac vascular conductance of 58 +/- 4 (SE), 48 +/- 3, 36 +/- 5, and 16 +/- 3% at rest, 3 miles/h and 0% grade, 6 miles/h and 0% grade, and 6 miles/h and 15% grade, respectively. These data demonstrate that activation of postganglionic sympathetic nerves with DMPP caused vasoconstriction in the skeletal muscle vasculature at rest and during exercise. Additionally, the magnitude of vasoconstriction was inversely related to exercise intensity. These results support the concept of exercise sympatholysis.

Functional anatomy of the vagal innervation of the cervical trachea of the dog

The canine cervical trachea has been used for numerous studies regarding the neural control of tracheal smooth muscle. The purpose of the present study was to determine whether there is lateral dominance by either the left or right vagal innervation of the canine cervical trachea. In anesthetized dogs, pressure in the cuff of the endotracheal tube was used as an index of smooth muscle tone in the trachea. After establishment of tracheal tone, as indicated by increased cuff pressure, either the right or left vagus nerve was sectioned followed by section of the contralateral vagus. Sectioning the right vagus first resulted in total loss of tone in the cervical trachea, whereas sectioning the left vagus first produced either a partial or no decrease in tracheal tone. After bilateral section of the vagi, cuff pressure was recorded during electrical stimulation of the rostral end of the right or left vagus. At the maximum current strength used, stimulation of the left vagus produced tracheal constriction that averaged 28.5% of the response to stimulation of the right vagus (9.0 +/- 1.8 and 31.6 +/- 2.5 mmHg, respectively). In conclusion, the musculature of cervical trachea in the dog appears to be predominantly controlled by vagal efferents in the right vagus nerve.

Autonomic control of skeletal muscle blood flow at the onset of exercise

The purpose of this study was to determine whether the autonomic nervous system is involved in skeletal muscle vasodilation at the onset of exercise. Mongrel dogs (n = 7) were instrumented with flow probes on both external iliac arteries. Before treadmill exercise at 3 miles/h, 0% grade, hexamethonium (10 mg/kg) and atropine (0.2 mg/kg) or saline was infused intravenously. Ganglionic blockade increased resting heart rate from 87 +/- 5 to 145 +/- 8 beats/min (P < 0.01) and reduced mean arterial pressure from 100 +/- 4 to 88 +/- 5 mmHg (P < 0.01). During steady-state exercise, heart rate was unaffected by ganglionic blockade (from 145 +/- 8 to 152 +/- 5 beats/min), whereas mean arterial pressure was reduced (from 115 +/- 4 to 72 +/- 4 mmHg; P < 0.01). Immediate and rapid increases in iliac blood flow and conductance occurred with initiation of exercise with or without ganglionic blockade. Statistical analyses of hindlimb conductance at 5-s intervals over the first 30 s of exercise revealed a statistically significant difference between the control and ganglionic blockade conditions at 20, 25, and 30 s (P < 0.01) but not at 5, 10, and 15 s of exercise. Hindlimb conductance at 1 min of exercise was 9.21 +/- 0.68 and 11.82 +/- 1.32 ml. min(-1). mmHg(-1) for the control and ganglionic blockade conditions, respectively. Because ganglionic blockade did not affect the initial rise in iliac conductance, we concluded that the autonomic nervous system is not essential for the rapid vasodilation in active skeletal muscle at the onset of exercise in dogs. Autonomic control of skeletal muscle blood flow during exercise is manifested through vasoconstriction and not vasodilation.

Rapid vasodilation in response to a brief tetanic muscle contraction

To test the hypothesis that vasodilation occurs because of the release of a vasoactive substance after a brief muscle contraction and to determine whether acetylcholine spillover from the motor nerve is involved in contraction-induced hyperemia, tetanic muscle contractions were produced by sciatic nerve stimulation in anesthetized dogs (n = 16), instrumented with flow probes on both external iliac arteries. A 1-s stimulation of the sciatic nerve at 1. 5, 3, and 10 times motor threshold increased blood flow above baseline (P < 0.01) for 20, 25, and 30 s, respectively. Blood flow was significantly greater 1 s after the contraction ended for 3 and 10 x motor threshold (P < 0.01) and did not peak until 6-7 s after the contraction. The elevations in blood flow to a 1-s stimulation of the sciatic nerve and a 30-s train of stimulations were abolished by neuromuscular blockade (vecuronium). The delayed peak blood flow response and the prolonged hyperemia suggest that a vasoactive substance is rapidly released from the contracting skeletal muscle and can affect blood flow with removal of the mechanical constraint imposed by the contraction. In addition, acetylcholine spillover from the motor nerve is not responsible for the increase in blood flow in response to muscle contraction.

alpha-adrenergic vasoconstriction in active skeletal muscles during dynamic exercise

Sympathetic vasoconstriction in working muscles during dynamic exercise has been demonstrated by intra-arterial administration of alpha(1)-adrenergic antagonists. The purpose of this study was to examine the existence of alpha(1)- and alpha(2)-adrenergic receptor-mediated vasoconstriction in active skeletal muscles during exercise. Six mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs, and a catheter was inserted in one femoral artery. All dogs ran on a motorized treadmill at three exercise intensities (3 miles/h, 6 miles/h, and 6 miles/h at 10% grade) on separate days. After 5 min of exercise, a selective alpha(1)- (prazosin) or a selective alpha(2)-adrenergic antagonist (rauwolscine) was infused as a bolus into the femoral arterial catheter (only one drug per day). The doses of the antagonists were adjusted to maintain the same effective concentration at each exercise intensity. At the mild, moderate, and heavy workloads prazosin infusion produced immediate increases in iliac conductance of 65 +/- 9, 35 +/- 6, and 18 +/- 4% (means +/- SE), respectively, and increases in blood flow of 290 +/- 24, 216 +/- 23, and 172 +/- 18 ml/min, respectively. Rauwolscine infusion produced increases in conductance of 52 +/- 5%, 36 +/- 5%, and 26 +/- 3%, respectively, and blood flow increases of 250 +/- 34, 244 +/- 39, and 259 +/- 35 ml/min at the three workloads. Systemic blood pressure and blood flow in the contralateral iliac artery were unaffected by any of the antagonist infusions. These results demonstrate that there is ongoing alpha(1)- and alpha(2)-adrenergic receptor-mediated vasoconstriction in exercising skeletal muscles even at heavy workloads and that the magnitude of vasoconstriction decreases as exercise intensity increases.

alpha1-adrenergic-receptor responsiveness in skeletal muscle during dynamic exercise

Attenuation of sympathetic vasoconstriction (sympatholysis) in working muscles during dynamic exercise is controversial. One potential mechanism is a reduction in alpha1-adrenergic-receptor responsiveness. The purpose of this study was to examine alpha1-adrenergic-receptor-mediated vasoconstriction in resting and working skeletal muscles by using intra-arterial infusions of a selective agonist. Seven mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and a catheter in one femoral artery. A selective alpha1-adrenergic-receptor agonist (phenylephrine) was infused as a bolus into the femoral artery catheter at rest and during exercise. All dogs ran on a motorized treadmill at two exercise intensities (3 and 6 miles/h). Intra-arterial infusions of the same effective concentration of phenylephrine elicited reductions in vascular conductance of 76 +/- 4, 76 +/- 6, and 67 +/- 5% (P > 0.05) at rest, 3 miles/h, and 6 miles/h, respectively. Systemic blood pressure and blood flow in the contralateral iliac artery were unaffected by phenylephrine. These results do not demonstrate an attenuation of vasoconstriction to a selective alpha1-agonist during exercise and do not support the concept of sympatholysis.

Renal hemodynamic responses to dynamic exercise in rabbits

Cardiovascular hemodynamics, including renal blood flow, were measured in rabbits with one intact and one denervated kidney during various intensities of treadmill exercise. Within the first 10 s of exercise, there was rapid vasoconstriction in the innervated kidney associated with decreases in renal blood flow (range -10 to -17%). The vasoconstriction in the innervated kidney was evident at all workloads and was intensity dependent. There was no significant vasoconstriction or change in renal blood flow (range 0.5 to -3.1%) in the denervated kidney at the onset of exercise. However, a slowly developing vasoconstriction occurred in the denervated kidney as exercise progressed to 2 min at all workloads. Examination of responses to exercise performed under alpha-adrenergic blockade with phentolamine (5 mg/kg iv) revealed that the vasoconstriction in the innervated kidney at the onset of exercise and the delayed vasoconstriction in the denervated kidney were due primarily to activation of alpha-adrenergic receptors. In addition, a residual vasoconstriction was also present in the innervated kidney after alpha-adrenergic blockade, suggesting that, during exercise, activation of other renal vasoconstrictor mechanisms occurs which is dependent on the presence of renal nerves.

Poling forces during roller skiing: effects of technique and speed

PURPOSE

Although it has been reported that the majority of propulsive forces are generated through the poles with ski skating, no study has systematically examined poling forces among different skating techniques. The objective of the present study was to examine poling forces and timing during roller skiing on a 2.1% uphill.

METHODS

Nine highly skilled cross-country skiers roller skied at three paced speeds and maximal speed using the V1 skate (V1), V2-alternate (V2A), V2 skate (V2), and double pole (DP) techniques while poling forces and timing were measured with piezoelectric transducers.

RESULTS

Peak force (PF) values with the skating techniques were significantly lower than with DP and ranged from 18.9 +/- 3.1% of body weight (BW) to 31.5 +/- 5.6% BW across the speeds of the study. Average force over the entire cycle (ACF) increased with speed with DP, V2A and V1 (P < 0.01) but not with V2. PF and ACF were higher (P < 0.01) with V2 than V1 and V2A. Poling time was longer (P < 0.01) with V2A compared with V1 and V2.

CONCLUSIONS

The results of this study suggest that 1) the use of the upper body is greater with V2 than with other skating techniques while there is a relatively greater reliance on the lower body for generation of the additional propulsive forces required to increase velocity, and (2) poling forces do not appear to be as effectively applied with V2 as with V2A.

Poling forces during roller skiing: effects of grade

PURPOSE

A substantial proportion of the propulsive forces required for uphill skiing are generated from the upper body, but no study has systematically examined poling forces at different slopes. In the present experiment, poling forces and timing were examined during roller skiing on 2.1% and 5.1% uphills.

METHODS

Nine highly skilled cross-country skiers roller skied at paced submaximal and at maximal speeds using the V1 skate (V1) and double pole (DP) techniques. Poling forces and timing were measured with piezoelectric transducers.

RESULTS

Peak force (PF), average force (AF) and average force over the entire cycle (ACF) were significantly greater (P < 0.01) at the steeper grade with both techniques. Values for the ratio of V1 to DP did not differ between the two grades for PF, AF, and ACF but tended to increase with velocity for both techniques. With both V1 and DP, upper body recovery time was shorter (P < 0.01) at the steeper grade, and cycle rate was greater (P < 0.01) at the steeper grade.

CONCLUSIONS

We conclude that 1) the relative demands on the upper body with V1 compared with DP were similar between the two grades, and 2) the responses to an elevation in grade of increased poling forces, shortened poling recovery times, and increased cycle rate are comparable to the responses to an increase in speed.

Skeletal muscle vasodilation at the onset of exercise

The purpose of this study was to determine whether beta-adrenergic or muscarinic receptors are involved in skeletal muscle vasodilation at the onset of exercise. Mongrel dogs (n = 7) were instrumented with flow probes on both external iliac arteries and a catheter in one femoral artery. Propranolol (1 mg), atropine (500 microgram), both drugs, or saline was infused intra-arterially immediately before treadmill exercise at 3 miles/h, 0% grade. Immediate and rapid increases in iliac blood flow occurred with initiation of exercise under all conditions. Peak blood flows were not significantly different among conditions (682 +/- 35, 646 +/- 49, 637 +/- 68, and 705 +/- 50 ml/min, respectively). Although the doses of antagonists employed had no effect on heart rate or systemic blood pressure, they were adequate to abolish agonist-induced increases in iliac blood flow. Because neither propranolol nor atropine affected iliac blood flow, we conclude that activation of beta-adrenergic and muscarinic receptors is not essential for the rapid vasodilation in active skeletal muscle at the onset of exercise in dogs.

Cycle rate variations in roller ski skating: effects on oxygen uptake and poling forces

The purpose of this study was to examine the effect of cycle rate (CR) variations on the metabolic cost and upper body forces during roller skiing with the V2-alternate technique on flat terrain. Nine highly skilled cross-country skiers roller skied at a paced speed of 18.0+/-0.1 km x h(-1) using their chosen CR, and CRs that were 10% slower and 20% faster. Oxygen uptake (VO2) was determined through collection of expired gases into a meterological balloon and poling forces were measured with piezoelectric transducers during the last 30 s of each four minute trial of roller skiing. One-way repeated measures ANOVA revealed that VO2 varied significantly with CR (p=0.02) with the chosen CR being significantly lower than the higher CR (p < 0.05). Poling forces and poling time were not significantly different among the CR conditions. The present results demonstrate that 1) an alteration in cycle rate affects metabolic cost of roller ski skating, 2) skiers tend to naturally select the most economical cycle rate, and 3) moderate variations in cycle rate do not appear to affect propulsive force generation through the poles in roller skiing.

Effect of rolling resistance on poling forces and metabolic demands of roller skiing

OBJECTIVE

To examine the effect of an increase in roller ski rolling resistance on the physiological and upper body demands of roller skiing with the V2-alternate technique.

METHODS

Nine highly skilled cross-country skiers roller skied at three paced speeds on a flat oval loop using roller skis with high (HiR) and low (LowR) rolling resistance. Oxygen uptake (VO2), heart rate, and poling forces were measured during the last 30 s and rating of perceived exertion (RPE) was requested immediately after each 4-min bout of roller skiing.

RESULTS

VO2 and all force-related variables increased significantly with speed and were higher (P < 0.01) for HiR at given speeds. Poling time was similar between HiR and LowR, whereas poling recovery time was shorter (P = 0.0002) and cycle rate was higher (P = 0.002) for HiR. For given VO2 levels, peak and average forces, heart rates, and RPE values were similar between HiR and LowR, whereas average poling force across the cycle was greater (P = 0.006) and duty cycle (i.e., percentage of cycle when poling forces were applied) was higher (P = 0.0001) with HiR.

CONCLUSIONS

1) The decrease in poling recovery time and increase in cycle rate associated with an increase in roller ski rolling resistance is comparable to the effect previously observed from increasing grade and probably occurs as a means of limiting deceleration. 2) Since changes in rolling resistance do not alter the relationships of RPE and heart rate with VO2, the central cardiovascular adaptations from roller ski training should not be affected by the rolling resistance of the roller skis. 3) Higher resistance roller skis are likely to induce greater upper body aerobic adaptations than lower resistance roller skis.

Hypoxia causes apnea during epidural anesthesia in rabbits

BACKGROUND

Although pulmonary function is minimally changed by neuraxial blockade in most cases, ventilatory arrest may ensue in rare cases. The authors examined the mechanism of apnea in a rabbit model of sudden ventilatory arrest during the combination of epidural anesthesia and hypoxia.

METHODS

Rabbits were studied during alpha-chloralose sedation and spontaneous ventilation through a tracheostomy tube. Heart rate and mean arterial pressure were monitored by intraarterial cannulation. Respiratory rate and tidal volume were measured by pneumotachograph. Responses were recorded during administration of oxygen at inspired oxygen concentrations of 11% for 2.5 min and 0% for 40 s, before and after either thoracolumbar epidural blockade (0.4 ml/kg lidocaine, 1.5%) or intramuscular lidocaine (15 mg/kg). In a third group of animals, epinephrine was given intravenously during epidural blockade to return mean arterial pressure to baseline values before hypoxia. In a fourth group of animals, which did not get lidocaine, sympathetic blockade and hypotension were produced with intravenously administered trimethaphan rather than epidural blockade.

RESULTS

Thoracolumbar epidural anesthesia decreased mean arterial pressure from 76 +/- 4 mmHg (mean +/- SE) to 42 +/- 2 mmHg. Apnea during hypoxia occurred in 90% of these animals (nine of ten) but in only 11% of animals (one of nine) after intramuscularly administered lidocaine (P < 0.01). Treatment of epidural hypotension with epinephrine prevented apnea (zero of nine animals). Apnea during hypoxia occurred in 50% (three of six) of animals given trimethaphan. Apnea in all groups was sudden in onset, with no preceding decreases in respiratory rate or tidal volume.

CONCLUSIONS

Epidural anesthesia results in a narrowed margin of safety for oxygen delivery to the brain and predisposes subjects to ventilatory arrest during hypoxia. This results from the combined effects of decreased blood oxygen content, which is due to decreased inspired oxygen concentration superimposed on circulatory depression due to neural blockade.

Physiological effects of technique and rolling resistance in uphill roller skiing

OBJECTIVE

The double pole technique (DP) has been shown to be more economical than the V1 skate technique (V1 ) on flat terrain. The objective of the present study was to compare these two techniques during uphill roller skiing. In addition, the physiological effects of changing roller ski rolling resistance was examined for V1.

METHODS

Five female and five male competitive cross-country skiers roller skied 4-min bouts on a 5.2% incline while physiological measurements were made.

RESULTS

Oxygen uptake (VO2) values averaged 8% greater (P = 0.0004) with V1, whereas rating of perceived exertion (RPE) and blood lactate concentrations were higher (P < or = 0.002) with DP. Doubling the dynamic friction coefficient of the roller skis, which increased external power output by 16-17%, resulted in VO2 values with V1 that averaged 13% higher (P = 0.0006). This magnitude of change in roller ski rolling resistance did not cause a statistical change in the relationship of VO2 with RPE.

CONCLUSIONS

These findings suggest that 1) grade has little effect on relative economies of DP and V1, possibly because of a lower effectiveness of force application with V1 when going uphill, and 2) large differences in roller ski rolling resistance should have no effect on the cardiovascular training adaptations that result from uphill roller skiing with V1.

Physiologic comparison of forward and reverse wheelchair propulsion

OBJECTIVES

Conventional wheelchair propulsion is physiologically demanding because of the small muscle mass that is used and the low mechanical efficiency of the movement. Previous research has suggested that a reverse wheeling technique might be more economical than conventional forward wheeling. The present study sought to compare the physiologic demands of forward and reverse wheeling techniques.

DESIGN

A repeated measures design was used to compare the dependent variables between forward and reverse wheeling techniques in the same subjects.

SETTING

Human exercise research laboratory.

PARTICIPANTS

Ten able-bodied men.

INTERVENTION

Subjects completed graded, discontinuous exercise tests on a wheelchair ergometer, using both forward and reverse wheeling techniques.

MAIN OUTCOME MEASURES

Oxygen uptake (VO2), ventilation (VE), and heart rate were measured during the last 30 seconds of each 3-minute exercise stage. Blood lactate concentration ([La]) and rating of perceived exertion (RPE) were determined immediately after each stage.

RESULTS

Repeated measures analysis of variance demonstrated that VO2, VE, heart rate, [La], and RPE were all significantly greater (p < .05) with reverse wheeling compared with forward wheeling. VO2, values with reverse wheeling averaged 9% higher than forward wheeling at identical power outputs.

CONCLUSIONS

Reverse wheelchair propulsion is physiologically more demanding than conventional forward wheelchair propulsion and does not appear to offer potential for improving the economy of wheelchair propulsion.

Autonomic control of skeletal muscle vasodilation during exercise

Despite extensive investigation, the control of blood flow during dynamic exercise is not fully understood. The purpose of this study was to determine whether beta-adrenergic or muscarinic receptors are involved in the vasodilation in exercising skeletal muscle. Six mongrel dogs were instrumented with ultrasonic flow probes on both external iliac arteries and with a catheter in a branch of one femoral artery. The dogs exercised on a treadmill at 6 miles/h while drugs were injected intra-arterially into one hindlimb. Isoproterenol (0.2 microg) or acetylcholine (1 microg) elicited increases in iliac blood flow of 89.8 +/- 14.4 and 95.6 +/- 17.4%, respectively, without affecting systemic blood pressure or blood flow in the contralateral iliac artery. Intra-arterial propranolol (1 mg) or atropine (500 microg) had no effect on iliac blood flow, although they abolished the isoproterenol and acetylcholine-induced increases in iliac blood flow. These data indicate that exogenous activation of beta-adrenergic or muscarinic receptors in the hindlimb vasculature increases blood flow to dynamically exercising muscle. More importantly, because neither propranolol nor atropine affected iliac blood flow, we conclude that beta-adrenergic and muscarinic receptors are not involved in the control of blood flow to skeletal muscle during moderate steady-state dynamic exercise in dogs.

Sympathetic vasoconstriction in active skeletal muscles during dynamic exercise

Studies utilizing systemic administration of alpha-adrenergic antagonists have failed to demonstrate sympathetic vasoconstriction in working muscles during dynamic exercise. The purpose of this study was to examine the existence of active sympathetic vasoconstriction in working skeletal muscles by using selective intra-arterial blockade. Six mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and with a catheter in one femoral artery. All dogs ran on a motorized treadmill at three intensities on separate days. After 2 min, the selective alpha 1-adrenergic antagonist prazosin (0.1 mg) was infused as a bolus into the femoral artery catheter. At mild, moderate, and heavy workloads, there were immediate increases in iliac conductance of 76 +/- 7, 54 +/- 11, and 22 +/- 6% (mean +/- SE), respectively. Systemic blood pressure and blood flow in the contralateral iliac artery were unaffected. These results demonstrate that there is sympathetic vasoconstriction in active skeletal muscles even at high exercise intensities.

Acute effects of ski waxing on pulmonary function

The objective of this study was to determine whether pulmonary function is acutely affected by moderate exposure to ski waxing. Ten healthy nonsmoking young adult volunteers were exposed to 45 min of ski waxing in a small unventilated room. The exposure occurred in pairs with one individual performing the waxing while the other overlooked the waxing process. During the period of waxing, two pairs of cross-country skis were waxed with a paraffin wax and then scraped and brushed, and two pairs of cross-country skis were waxed with a fluorinated wax and then brushed. Spirometry and single-breath carbon monoxide lung diffusion capacity (DLCO) were measured immediately before and after exposure to ski waxing, and again 5-6 h after waxing. A subset of five subjects repeated the measurements on a separate day without receiving exposure to ski waxing. Data were analyzed with repeated measures ANOVA. Exposure to ski waxing induced no significant changes in spirometry and DLCO measurements. We conclude that moderate exposure to ski waxing has no significant acute effect on lung function.

Muscle chemoreflex increases renal sympathetic nerve activity during exercise

Activation of the muscle chemoreflex increases sympathetic drive to skeletal muscle in humans. This study investigated whether activation of the muscle chemoreflex augments the renal sympathetic nerve activity (RSNA) response to dynamic exercise in rabbits. The muscle chemoreflex was evoked by hindlimb ischemia during exercise on a motorized treadmill. Seven New Zealand White rabbits performed a nonischemic control protocol and a hindlimb ischemia protocol in which terminal aortic blood flow (Qta) was reduced to 51 +/- 2% of preocclusion Qta by partial aortic occlusion after 1.5 min of exercise. Mean arterial pressure (MAP), heart rate, RSNA and Qta increased in response to exercise and were similar between trials during the first 1.5 min of exercise. In the control trial, Qta, MAP, and RSNA were stable at an elevated level through an additional 3.5 min of exercise. Hindlimb ischemia produced a potent pressor response that plateaued after 2.5 min (delta + 17 +/- 4 mmHg, where delta designates change). RSNA began to increase after 1.5 min of ischemic exercise and was significantly elevated relative to preocclusion RSNA at 2.5 (delta + 25 +/- 9%) and 3.5 (delta + 47 +/- 12%) min of occlusion. These results suggest that the muscle chemoreflex can augment sympathoexcitatory drive to the kidney during dynamic exercise.

Does the amount of exercising muscle alter the aerobic demand of dynamic exercise?

The primary purpose of this study was to determine if the aerobic demand for production of specified power outputs is altered by distribution of work between the arms and legs compared with when all the work is performed by the legs. Because of the important exercise training implications, a secondary purpose of this study was to determine if the exercising muscle mass affects the cardiorespiratory demands at specified rating of perceived exertion (RPE) levels and blood lactate concentrations. Nine healthy adults completed leg cycling and combined arm and leg exercise on an Airdyne using a discontinuous protocol. Repeated measures ANOVA revealed that oxygen uptake for the combined arm and leg exercise averaged 0.04 1.min-1 greater (p < 0.05) than for leg cycling at the same external power outputs. However, RPE levels at specified power outputs were lower (p < 0.05) with combined arm and leg exercise than leg cycling. At specified RPE levels and blood lactate concentrations, oxygen uptake and heart rate values were higher (p < 0.05) for combined arm and leg exercise than leg cycling. From these findings we conclude that: (1) the addition of arm exercise to leg cycling results in a reduction in RPE, but a minimal increase in oxygen consumption to perform a given power output, and (2) if training intensity is established by RPE or blood lactate concentration, use of muscle mass larger than that used in leg cycling should allow a greater cardiorespiratory training effect.

Energy expenditure with indoor exercise machines

OBJECTIVE

To compare the rates of energy expenditure at given rating of perceived exertion (RPE) levels among 6 different indoor exercise machines.

DESIGN

Repeated measures design.

PARTICIPANTS

Healthy young-adult volunteers, including 8 men and 5 women.

INTERVENTIONS

Subjects underwent a 4-week habituation period to become familiar with the RPE scale and exercise on an Airdyne, a cross-country skiing simulator, a cycle ergometer, a rowing ergometer, a stair stepper, and a treadmill. Following habituation, each subject completed an exercise test with each exercise machine. The exercise test comprised 3 stages of 5 minutes at self-selected work rates corresponding to RPE values of 11 (fairly light), 13 (somewhat hard), and 15 (hard). Oxygen consumption, from which the rate of energy expenditure was calculated, was measured during the last minute of each 5-minute exercise stage. Heart rate was measured during the last minute of each stage of the exercise test, and blood lactate levels were obtained immediately after each exercise stage.

MAIN OUTCOME MEASURE

Rate of energy expenditure at specified RPE values.

RESULTS

Rates of energy expenditure at a given RPE varied by 1093 kJ/h (261 kcal/h) for the exercise machines. The treadmill induced higher (P < .05) rates of energy expenditure for fixed RPE values than all other exercise machines. The cross-country skiing simulator, rowing ergometer, and stair stepper induced higher (P < .05) rates of energy expenditure than the Airdyne and cycle ergometer. Heart rate varied significantly (P < .01) among exercise machines, with the highest values associated with the treadmill and the stair stepper. Lactate concentration varied significantly (P = .004), with highest values associated with use of the stair stepper and the rowing ergometer.

CONCLUSIONS

Under the conditions of the study, the treadmill is the optimal indoor exercise machine for enhancing energy expenditure when perceived exertion is used to establish exercise intensity.

Muscle chemoreflex causes renal vascular constriction

The purpose of this study was to investigate the effects of the muscle chemoreflex on vascular conductance in innervated and denervated kidneys. During each experiment, six dogs ran at 10 km/h for 8-16 min, and the muscle chemoreflex was stimulated by reducing hindlimb blood flow (HLBF) (0%-74%) at 4-min intervals. Small reductions in HLBF did not cause changes in arterial blood pressure or renal vascular conductance. However, further reductions of HLBF caused increases in arterial blood pressure and decreases in renal vascular conductance. Decreases in renal vascular conductance occurred in the denervated kidneys when the HLBF was reduced below 1,500 +/- 215 ml/min and occurred in the innervated kidneys when HLBF was reduced below 1,402 +/- 161 ml/min. There was not a significant difference between the reductions in HLBF required to cause a decrease in vascular conductance in the innervated and denervated kidneys. These results demonstrate that reductions in HLBF cause decreases in renal vascular conductance, which are not dependent on renal sympathetic nerve activity.

Relationships among heart rate, lactate concentration, and perceived effort for different types of rhythmic exercise in women

OBJECTIVE

Exercise training intensity for aerobic conditioning is typically established by heart rate (HR), oxygen uptake, or rating of perceived exertion (RPE). Recent research, however, suggests that the optimal training intensity may be more appropriately established from measurements of blood lactate concentration ([La]). This study examined the relationships among three of these training intensity variables--HR, RPE, and [La]--for six modes of rhythmic exercise.

DESIGN

Ten healthy women subjects underwent a 4-week habituation period to become familiar with the RPE scale and exercise on a treadmill, cycle ergometer, rowing ergometer, Airdyne, stairstepper, and cross-country skiing simulator. Following habituation, each subject underwent graded discontinuation exercise testing on each mode. HR was measured during the last minute of each 4-minute stage. Immediately after each stage, RPE was requested and blood was collected for analysis of [La]. Data were analyzed with repeated measures ANOVA.

RESULTS

For given RPE values, the treadmill induced higher (p < .05) HR values compared with the cycle and rowing ergometers, and the cycle ergometer induced lower (p < .05) HR values compared with the treadmill, Airdyne, stairstepper, and cross-country skiing simulator. The relationships of [La] with RPE were similar among modes except for the cross-country skiing simulator, which induced a lower (p < .05) [La] for a given RPE.

CONCLUSIONS

Since the relationships of HR and [La] with RPE are not the same for all forms of rhythmic exercise that use a large muscle mass, we conclude that mode specificity should be considered when prescribing aerobic exercise.

Delta efficiency of uphill roller skiing with the double pole and diagonal stride techniques

Delta efficiencies for uphill roller skiing with the double pole (DP) and diagonal stride (DS) techniques were determined among 4 female and 4 male cross-country ski racers in order to examine for differences between techniques and between the sexes. Each skier roller-skied on a motorized ski-treadmill at 1.7% and 7.1% grades with both techniques at 2 to 4 different speeds. Steady-state oxygen uptake values were used to calculate the differences in metabolic requirements for roller skiing at the 2 grades (delta E). The differences in external work rates between the 2 grades (delta W) were calculated from the work rates for overcoming rolling resistance and elevating the transported mass against gravity. Delta efficiencies (delta W/ delta E) ranged from 14 to 36%, were significantly greater (p < 0.001) for DS than DP, and showed a significant (p < 0.01) velocity effect for DS. Delta efficiencies were 27% greater (p < 0.05) for the women compared with the men for DP, and significant (p < 0.05) correlations were found between efficiency for DP and body mass. This suggests that the higher efficiency with DP for female skiers is at least partially due to their lower body mass.

Lactate response to uphill roller skiing: diagonal stride versus double pole techniques

The purpose of this experiment was to investigate the lactate responses to roller skiing with double pole and diagonal stride techniques in eight collegiate or national level cross-country ski racers. Four-minute exercise stages were performed on a ski treadmill at 67, 94, 121, 148, and 174 m.min-1 on a 1.7% grade and at 67, 94, and 121 m.min-1 on a 7.1% grade. Whole blood lactate concentration, heart rate, oxygen consumption (VO2) and rating of perceived exertion (RPE) were determined at each exercise stage. Blood lactate concentrations were not significantly different between double poling and diagonal striding at the 1.7% grade. However, the blood lactate concentrations were higher during double poling at the 7.1% grade for all speeds. Blood lactate concentrations were also higher for double poling at the 7.1% grade when compared with diagonal striding at 70% of technique specific peak VO2, a heart rate of 145 and a RPE of 12. We conclude that blood lactate concentrations do not offer physiological justification for choosing one technique over the other when skiing on low grades, but low blood lactate concentrations may provide a physiological advantage for diagonal striding on steep grades.

Phenyl biguanide does not inhibit locomotion in conscious rabbits

Stimulation of cardiopulmonary vagal C fibers with phenyl biguanide (PBG) reflexly inhibits locomotion in addition to causing depression of blood pressure (BP), heart rate (HR), and respiration in cats and rats. We investigated whether PBG caused somatomotor inhibition during exercise in the rabbit, a species in which it is known that the hemodynamic and respiratory responses to PBG are mediated by cardiac rather than by pulmonary receptors. In eight New Zealand White rabbits, BP, HR, and hindlimb electromyographic (EMG) responses to 60 and 120 micrograms/kg PBG and saline vehicle were evaluated during two separate 3-min exercise bouts at 10 m/min at 0% grade. During exercise, 60 micrograms/kg PBG decreased BP (-27 +/- 4 mmHg) and HR (-95 +/- 16 beats/min) but did not inhibit locomotion as suggested by the EMG response (+112 +/- 8% of preinfusion EMG). Hemodynamic and EMG responses to 120 micrograms/kg PBG were similar to 60 micrograms/kg PBG. Saline infusion during exercise had no effect on HR, BP, or locomotion (+114 +/- 8% of preinfusion EMG). Locomotion is not inhibited by PBG in rabbits, which suggests that PBG-induced reflex somatomotor inhibition observed in other species is primarily mediated by pulmonary rather than by cardiac receptors.

Effects of pulmonary denervation on renal sympathetic and heart rate responses to hypoxia

We hypothesized that the renal sympathetic nerve activity (RSNA) response to hypoxia is attenuated because of stimulation of pulmonary receptors by the increase in ventilation. RSNA was measured during 20 min of severe hypoxia (8% O2) in conscious New Zealand White rabbits with intact lung innervation and in rabbits with surgical denervation of the lungs (LDX). LDX decreased resting breathing frequency but had no effect on resting mean arterial pressure (MAP), heart rate (HR), or RSNA. In intact rabbits, 4 min of hypoxia resulted in elevated RSNA (from 14 +/- 2 to 29 +/- 3% of smoke-elicited maximum), bradycardia (delta-65 +/- 12 beats/min), and no change in MAP (delta 2 +/- 2 mmHg). Bradycardia diminished with time, but elevated RSNA was maintained throughout the 20-min exposure. LDX enhanced the initial bradycardia (delta-113 +/- 11 beats/min, P < 0.01) but had no effect on the RSNA response (35 +/- 2% of maximum) to hypoxia. LDX did not alter steady-state responses of HR or RSNA, but MAP declined over time (-11 +/- 2 mmHg). These results suggest that in conscious rabbits pulmonary receptors have a minor influence on control of sympathetic activity to viscera during severe hypoxemia.

Effect of an abdominal binder during wheelchair exercise

The purpose of this study was to determine whether use of an abdominal binder would affect oxygen uptake, trunk range of motion, and duration of the stroke phase during wheelchair propulsion. The subjects were six paraplegic wheelchair athletes with T1-T6 injuries and no abdominal muscle function. Each subject performed two trials, one while wearing the binder and one without the binder. Each trial consisted of submaximal and maximal exercise tests conducted on wheelchair rollers. Oxygen uptake was determined by open circuit spirometry while heart rate was determined by telemetry. Max VO2 values averaged 2.51 l.min-1 while average maximum heart rate values were 190 b.min-1. A 3-D video-based motion analysis system was used to obtain kinematic parameters of wheelchair propulsion. In general, 30% of the cycle time was comprised of the stroke phase, while 70% was comprised of the recovery phase across speeds. There were no statistically significant effects of the abdominal binder on any of the cardiovascular or kinematic variables at submaximal or maximal levels of exercise. Under the conditions of this laboratory investigation, it appears that an abdominal binder does not alter physiological or selected biomechanical measures in highly trained athletes.

Cold-induced responses in the upper respiratory tract

Recent investigations have shown that the prevalence of bronchial asthma is higher among skiers exposed to cold and dry air than among nonskiers. The upper airway passages are responsible for warming and humidifying the inhaled air. During exercise in cold and dry air, warming and humidifying of the inhaled air continues in the bronchial tree. Under these conditions both nasal and bronchial mucosa are cooled by inspiratory air and remain cooled throughout the respiratory cycle. The air which reaches the bronchoalveolar air space is at body temperature and fully saturated in all conditions. In this article we briefly review the studies carried out regarding the effects of cold air inhalation on the upper respiratory tract.

Pigeon-serum-induced hypersensitivity pneumonitis in the dog

Pigeon serum (PS) is one of the most common causes of hypersensitivity pneumonitis (HP). PS-induced HP was examined in a dog model. The dogs (n = 6) were immunized by i.m. injections of PS, followed by insufflation with aerosolized PS, while all control dogs (n = 3) received saline only. All animals insufflated with PS developed tachypnea 2-4 h after PS inhalation. After PS insufflation, a significant decrease in arterial oxygen tension (PaO2) was detected in sensitized dogs. No change in PaO2 was detected in sensitized dogs after saline or in the controls after PS insufflation. In intradermal skin tests with PS antigen, a positive skin reaction was found in 3/6 dogs in 30 min, and in 5/6 dogs in 6 and 48 h after the PS injections. Sensitized dogs showed a significant increase in PS-specific IgG in serum and lavage fluid (LF). In LF of sensitized dogs, an increase in the percentage of lymphocytes, eosinophils, and neutrophils was detected. Sensitized dogs developed chronic interstitial inflammation with lymphocytes, macrophages, plasma cells, and eosinophils in lungs. Granulomas with lymphocytes, histiocytes, and giant cells were detected in both the interstitium and the bronchiolar wall in the lungs of sensitized dogs. PaO2 was lowest in dogs showing the most severe interstitial inflammation in the lungs. The results indicate that dogs can be successfully used in immunologic and physiologic studies of PS-induced HP.

Muscle chemoreflex alters vascular conductance in nonischemic exercising skeletal muscle

Previous studies have shown that the muscle chemoreflex causes an augmented blood pressure response to exercise and partially restores blood flow to ischemic muscle. The purpose of this study was to investigate the effects of the muscle chemoreflex on blood flow to nonischemic exercising skeletal muscle. During each experiment, dogs ran at 10 kph for 8-16 min and the muscle chemoreflex was evoked by reducing hindlimb blood flow at 4-min intervals (0-80%). Arterial blood pressure, hindlimb blood flow, forelimb blood flow, and forelimb vascular conductance were averaged over the last minute at each level of occlusion. Stimulation of the muscle chemoreflex caused increases in arterial blood pressure and forelimb blood flow and decreases in forelimb vascular conductance. The decrease in forelimb vascular conductance demonstrates that the muscle chemoreflex causes vasoconstriction in the nonischemic exercising forelimb. Despite the decrease in vascular conductance, the increased driving pressure caused by the pressor response was large enough to produce an increased forelimb blood flow.

Restricted postexercise pulmonary diffusion capacity does not impair maximal transport for O2

We evaluated whether the postexercise reduction of pulmonary diffusion capacity for carbon monoxide (DLco) is influenced by a second bout of rowing and whether it affects arterial O2 tension during maximal exercise. After exercise, DLco was reduced [from a median of 37 (range of 30-44) to 34 (27-40) ml.min-1.mmHg-1; n = 21; P < 0.001], and both the membrane diffusion capacity [from 80 (58-139) to 68 (54-104) ml.min-1.mmHg-1] and the pulmonary capillary blood volume [from 88 (74-119) to 79 (61-121) ml; P < 0.01] were affected. A second bout of exercise did not influence DLco or membrane diffusion capacity (n = 7), but during both bouts arterial O2 tension was reduced [from 105 (91-110) to 91 (77-102) Torr; P < 0.001] and arterial O2 saturation decreased [from 0.98 (0.97-0.99) to 0.95 (0.86-0.96); P < 0.001]. Furosemide (iv) did not affect DLco (n = 7), suggesting that it was influenced by the central blood volume rather than by pulmonary edema.

Physiological comparison of uphill roller skiing: diagonal stride versus double pole

The physiological responses to treadmill roller skiing with the double pole (DP) and diagonal stride (DS) techniques were compared at 1.7% and 7.1% grades among eight cross-country ski racers. Oxygen uptake (VO2) requirements were found to be lower (P < 0.05) for DP at the 1.7% grade, but similar at the 7.1% grade. In contrast, ratings of perceived exertion (RPE) and percentages of technique-specific peak VO2 were similar between techniques at the 1.7% grade, and lower (P < 0.05) for DS at the 7.1% grade. RPE and percentages of technique-specific peak VO2 were strongly correlated (r = 0.89). The primary findings indicate that 1) the economies for DP and DS are dependent upon the incline, 2) it is possible for the economy of DP to be greater than DS although the percentages of technique-specific peak VO2 are similar, and 3) the perceived effort associated with the use of DP and DS reflects the percentage of technique-specific peak VO2.

Arterial blood pressure response to rowing

Ten male oarsmen performed a 6-min bout of "all-out" exercise on a rowing ergometer in the laboratory. Intraarterial blood pressure was recorded from a catheter inserted percutaneously into the radial artery. Mean arterial pressure increased only modestly from 110 +/- 13 to 122 +/- 24 mm Hg (P < 0.05). Large fluctuations in pressure were superimposed on the normal blood pressure waveform during rowing. These rhythmic pressure fluctuations exhibited a one-to-one coupling with stroke rate and were 2-3 times the magnitude of the normal pulse pressure. Thus, the effective pulse pressure during the 1st minute of rowing (112 +/- 11 mm Hg) was markedly higher (P < 0.01) than the pulse pressure at rest (45 +/- 5 mm Hg) and remained so throughout the exercise bout. In five additional subjects in which central venous pressure (CVP) was measured, large stroke-related fluctuations in pressure were also seen in the CVP waveform. Similar fluctuations in blood pressure were observed during repetitive Valsalva maneuvers. These results suggest that the blood pressure response to rowing is principally influenced by a Valsalva-like maneuver performed at the catch of each stroke. The observed arterial pressure fluctuations may explain the degree of myocardial hypertrophy that occurs in the hearts of rowers.

Intrapericardial blocking agents have extracardiac effects in dogs

The purpose of this study was to determine if intrapericardial infusion of hexamethonium, propranolol, or atropine affected extracardiac receptors in anesthetized dogs. Intrapericardial hexamethonium (> or = 25 mg) decreased renal sympathetic nerve activity (RSNA) in a dose-dependent fashion. After 250 mg, RSNA began to decrease in 65 +/- 7 s. Whereas vagal stimulation caused a muscarinic receptor-mediated increase in tracheal smooth muscle tone (as indicated by a 9.6 +/- 1.1 mmHg increase in endotracheal cuff pressure), the increase in cuff pressure (1.8 +/- 0.4 mmHg) was attenuated after intrapericardial tropine (4 mg). When the ansa and vagus were stimulated simultaneously, beta-adrenergic receptor-mediated smooth muscle relaxation opposed the muscarinic receptor-mediated constriction resulting in an increase in cuff pressure of only 3.6 +/- 0.9 mmHg. After intrapericardial propranolol (8 mg), simultaneous ansa and vagal stimulation caused a 7.0 +/- 1.6 mmHg increase in cuff pressure, demonstrating that intrapericardial propranolol blocked beta-adrenergic receptor-mediated relaxation of tracheal smooth muscle. These results show that hexamethonium, atropine, and propranolol infused intrapericardially have extracardiac effects.

Cardiac receptors modulate the renal sympathetic response to dynamic exercise in rabbits

Activation of cardiac sensory receptors with vagal afferents can result in inhibition of sympathetic outflow to the peripheral circulation. This study investigated whether the regulation of renal sympathetic nerve activity (RSNA) during dynamic exercise was modulated by cardiac sensory receptors. RSNA, blood pressure, and heart rate were measured in seven New Zealand White rabbits during treadmill exercise while cardiac receptors were intact (saline), during cardiac neural block with 2% procaine (2% PCN), and during cardiac efferent receptor block with methscopolamine and atenolol (M + A). Drugs were infused into the pericardial space via a chronic catheter. Two exercise protocols were used: 7 m/min (5 min) and 12 m/min (2 min) at 0% grade. The increases in HR during exercise at 7 and 12 m/min were attenuated with 2% PCN or M + A. At 12 m/min, blood pressure was significantly lower with 2% PCN (76 +/- 4 mmHg) or M + A (76 +/- 3 mmHg) than with saline (86 +/- 2 mmHg). Abolition of cardiac afferent input with 2% PCN resulted in a potentiated RSNA response to exercise at 7 m/min (+134 +/- 37%) and 12 m/min (+234 +/- 45%) relative to saline (+62 +/- 24 and +101 +/- 28%) or M + A (+19 +/- 9 and +52 +/- 19%, P < 0.05). These results suggest that cardiac sensory receptors attenuate sympathetic drive to the kidney during dynamic exercise in conscious rabbits.

Maximal inspiratory pressure following endurance training at altitude

Effects of endurance training on maximal inspiratory pressure and fatigue were evaluated after 5 weeks. Twelve male and 9 female untrained subjects were matched in the three groups for sex and maximal oxygen uptake (VO2 max). Training was performed at 70% VO2max; 45 min day-1; 5 days week-1 (n = 7); and at the same relative (n = 7) and absolute (n = 7) work loads in a pressure chamber corresponding to 2500 m (560 mmHg). Work load was increased every week to maintain the training heart rate. Maximal respiratory pressure was measured at the mouth before and 30, 60 and 120 s after maximal exercise. With no significant difference between the three groups of subjects, VO2max increased from 2.96 (1.98-4.47) (median and range for 21 subjects) to 3.33 (2.50-4.72) 1 min-1 (p < 0.001) and ventilation (VE max) from 109 (57-147) to 123 (73-148) 1 min-1 (p < 0.001), while maximal heart rate decreased from 193 (180-211) to 192 (169-207) beats min-1 (p < 0.01). Maximal inspiratory pressure (87 (56-115) mmHg), inspiratory muscle fatigue (18 (-2-43)%, p < 0.001), and arterial oxygen tension during exercise (12.4 (9.9-15.6)kPa) were similar before and after training. The results demonstrate that training at simulated altitude at 2500 m does not increase VE max or VO2 max above the increases obtained from training at sea level. Furthermore, VEmax and VO2 max increased approximately 13% despite unchanged maximal inspiratory pressure and inspiratory muscle fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological responses to specific maximal exercise tests for cross-country skiing

The present study attempted to quantify differences in peak physiological responses to pole-striding (PS), double poling on roller skis (DP), and diagonal striding on roller skis (DS) during maximal exercise. Six expert cross-country ski racers (3 M, 3 F) with a mean age of 20.2 +/- 1.3 yrs served as subjects. Testing was conducted on a motorized ski treadmill with a tracked belt surface. Expired air was analyzed continuously via an automated open-circuit system and averaged each 20 s. Heart rate was monitored via telemetry and arterialized blood was collected within 1 min of test termination and analyzed immediately for lactate. Peak values for heart rate and blood lactate did not differ among techniques. Peak oxygen uptake was higher for PS and DS versus DP whereas no difference was found between PS and DS. The VO2peak for DP was 77 and 81% of VO2peak for PS and DS, respectively. It was concluded that despite similar peak heart rate and blood lactate values, DP elicits a lower VO2peak than DS or PS and that PS responses appear to closely reflect those of DS.