Does lung function limit performance in a 24-hour ultramarathon?

Based on observations of impaired lung function after marathon and ultramarathon running, it was hypothesized that the decline in running speed during a 24-h ultramarathon may be explained, in part, by ventilatory muscle fatigue. To test this hypothesis, ten competitors in the 1988 TAC/USA National 24-h Championship performed a battery of pulmonary function tests every 3 h during the race. The tests included measurement of inspiratory capacity, peak flow, forced vital capacity, forced expiratory volume in 1 sec, maximum voluntary ventilation for 12 sec (MVV12), and maximal respiratory pressures. Running speed was averaged over 3-h periods. MVV12 was significantly decreased (17%), but only after 24 h of running. All other ventilatory measures tended to decrease over time but the changes were not significant. However, after correcting for between-subject differences in running speed, the variance in MVV12 accounted for 39% (P less than 0.0001) of the variance in running speed. It was concluded that the decrease in ventilatory muscle endurance may constrain running speed in extremely prolonged running events.

The mechanism of mucus clearance in cough

An instability resembling an avalanche is proposed as the mechanism by which mucus is expelled from the respiratory tract during cough. The cough event was simulated in a model airway. In these experiments, air was forced through a channel whose walls were lined with a non-Newtonian material rheologically similar to tracheal mucus. Frames from high-speed cine photographs showed an unstable event which began as an undulation of the free surface and progressed to a catastrophic clearance of the channel. Measurements of the longitudinal pressure gradient support the hypothesis that the clearance event is initiated when the total stress applied to the mucus analog exceeds its finite yield stress. A continuum model predicts that yielding occurs within the bottom layers of the mucus analog. Calculations based upon estimates of tracheal geometry and air flow show that the clearance event studied here would be expected to occur during a cough but not during normal breathing. Experiments also show that a lubricant introduced between the channel walls and the mucus blanket can reduce the air flow rate required to precipitate the clearance.

Total respiratory resistance and reactance in patients with diffuse interstitial lung disease

In 54 patients with interstitial lung diseases and no signs of airway obstruction we measured lung volumes, maximal expiratory flows, diffusing capacity (DLCO), total respiratory resistance (Rrs) and reactance (Xrs) between 4 and 26 Hz by means of the forced oscillation technique. In all patients DLCO was less than 75% of the expected value. Patients were classified into two groups depending on total lung capacity (TLC): group A with TLC less than 80% of expected, and group B with TLC of 80% or more. Group A demonstrated a decrease of Xrs especially at low frequencies, with small, not significant changes in Rrs. In the patients in this group with the lowest values of TLC (less than 50%), we observed an increase of Rrs at low frequencies causing a negative frequency dependence of Rrs. In group B no distinct changes of Rrs and Xrs occurred. Canonical correlation analysis between routine lung function data and forced oscillation parameters, showed tight correlations between TLC in absolute value or VC in percent of the predicted value on the one hand and average level of Xrs and average slope of Xrs (and Rrs) vs frequency curves on the other hand. Measurements of lung mechanics in five additional patients and comparison with a model of the respiratory system suggest that the changes of Rrs and Xrs are not explained totally by the observed increase in lung tissue resistance and decrease in lung compliance. The observed changes in Rrs and Xrs are not specific for restrictive lung disorders; similar changes are met also in moderately advanced obstructive diseases.

Continuous oxygen insufflation in addition to IPPV causes air trapping in a mechanical lung model

It has previously been reported that continuous insufflation of either supracarinal or subcarinal oxygen in addition to intermittent positive-pressure ventilation (IPPV) in patients under general anesthesia, and in critically ill patients in the intensive care unit, causes increased proximal airway pressure, decreased systemic blood pressure, and decreased cardiac output. The investigators hypothesized that these deleterious hemodynamic effects were due to intrapulmonary air trapping, resulting in an increased distal intrapulmonary pressure and volume. The purpose of this study was to test this hypothesis in an appropriate mechanical lung model. The study determined end-inspiratory and end-expiratory lung pressures and volumes during eight experimental sequences: (1) IPPV alone; (2) insufflation of oxygen alone at 2.5, 5.0, and 10.0 L/min (O2-2.5, 5.0, 10.0); (3, 4, and 5) IPPV plus insufflation of oxygen (IPPV + O2-0.0, 2.5, 5.0, 10.0) through a supracarinal catheter (sequence 3), subcarinal catheters (sequence 4), and through a CO2 sampling port of an endotrachael tube (sequence 5); (6 and 7) IPPV + O2-5.0 with increased expiratory time caused by an increased inspiratory flow rate (sequence 6) and a decreased respiratory rate (sequence 7); (8) IPPV + O2-5.0 with increased airway diameter. Experimental sequences 1 and 2 resulted in no increases or minimal ones in lung pressure and volume, respectively. With each insufflation catheter system (sequences 3, 4, and 5), each incremental increase in insufflation flow rate resulted in significant increases in lung pressure and volume. Increasing expiratory times (sequences 6 and 7 compared with 3, 4, and 5) decreased lung pressure and volume. Increasing the airway diameter (sequence 8) had only slight effect on lung pressure and volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain cooling and respiratory heat exchange in camels during rest and exercise

Respiration in relation to brain temperature (Tb) and body temperature (Tc) were investigated in two camels at rest and one during exercise (running at 10 km/h). The animals were subjected to natural ambient conditions (day: 25-30 degrees C, relative humidity (RH) about 65%; night: 15-20 degrees C, RH approx. 90%). They were studied when fully hydrated and during progressive dehydration by up to 15% of initial weight. At low Tc (less than 38 degrees C) Tb greater than Tc by approximately 0.2 degrees C, at higher Tc significant brain cooling was observed by as much as 1.5 degrees C during exercise. Minute ventilation (VE) and respiratory rate (f) increased with Tc such that tidal volume was constant and similar at rest and during exercise (Tc-Tb) increased linearly with f and hence VE. The cooling, dependent on turbinate heat exchange was related to certain features of the air flow pattern and f which have also been described in other large mammals.

Flow distribution through human and canine airways during inhalation and exhalation

Airflow distribution through the tracheobronchial tree is influenced by many factors. In a hollow cast of the central airways, the only factors involved are resistance and inertia of the airflow. Distribution of steady flow during both inhalation and exhalation was measured at different total flow rates in human and canine tracheobronchial casts. The resulting airflow rates in peripheral segments were measured with a sensitive apparatus, which did not disturb the distribution of flow. Inertia of the airflow was found to be small but significant in airways of the human cast and substantially greater in the canine airway cast than in the human cast during inhalation. The influence of airflow inertia during inhalation was largely responsible for the different distributions of flow during inhalation and exhalation through the airway casts. Airflow resistance was found to be considerably greater during exhalation and may have contributed to the redistribution of flow. The forces involved are small but should be considered when modeling the in vivo distribution of airflow.

Four and six parameter models of forced random noise respiratory impedance in normals

Total respiratory impedance has been measured between 3-42 Hz by the forced random noise technique, in 15 subjects breathing either air or a helium oxygen mixture in three experimental conditions: at basal state, and then with a resistor or a tube added at the mouth. Impedance is modelled, either by a 4-parameter model (M4), derived from the series model (resistance, inertance, compliance) by making resistance a linear function of frequency; or by a 6-parameter model (M6) including a central compartment (airway resistance and gas inertance), and a tissue compartment (resistance, inertance and compliance in series) placed in parallel with alveolar gas compliance. The additive resistance is perfectly evaluated by both models, whereas the additive inertance is not accurately estimated by the model M6, the fitting of which combines the real and imaginary parts of impedance. Resistance extrapolated at zero frequency on the one hand, inertance of M4 and central inertance of M6 of the other, are highly correlated. However, changes in some parameters of both models according to the experimental conditions are difficult to explain on physiological grounds. We conclude that the model M6 cannot be easily and accurately identified over such a limited frequency range, at least in normals, while the model M4 yields a simplified description of impedance which may be sufficient for diagnostic purposes.

In vivo exposure to hyperoxia increases airway responsiveness in rats. Demonstration in vivo and in vitro

Studies regarding O2-induced lung injury have concentrated on damage to alveolar structures and pulmonary vasculature without consideration of alterations that may be occurring in airways. This study was undertaken to determine the effects of in vivo hyperoxic exposure on airway responses to excitatory stimuli in intact, anesthetized rats and in intrapulmonary bronchi isolated from hyperoxia-exposed rats. Using lung conductance (G1) as an index of bronchoconstriction, intravenously administered 5-hydroxytryptamine (5HT) elicited greater bronchoconstrictor responses in anesthetized, mechanically ventilated rats that had been exposed to 85% O2 for 7 days rather than to air. Further, airways of hyperoxia-exposed rats were more sensitive to the effects of intravenously administered 5HT as evidenced by the lower log dose of 5HT required to decrease G1 30%. Cylindrical segments of intrapulmonary bronchi isolated from hyperoxia-exposed rats were more responsive to the contractile effects of 5HT and electrical field stimulation. However, no differences in responsiveness to bethanechol or KCl were observed between the two groups. The log concentration of 5HT and the log frequency of electrical field stimulation that elicited half-maximal responses were smaller in bronchi isolated from hyperoxia-exposed animals, indicating an increase in sensitivity of the airways to these stimuli. These results suggest that prolonged exposure to greater than ambient levels of O2 can alter airway function; however, the mechanism responsible for these changes remains to be determined.

Airway insufflation: physiologic effects on acute and chronic gas exchange in humans

Reduction in dead space through conventional tracheostomy has been used to treat patients with chronic CO2 retention. The insufflation of air directly into the trachea by transtracheal catheter (airway insufflation, AI) provides reductions in dead space as great or greater than those of tracheostomy. The physiologic effects of AI on gas exchange have not been adequately studied because instillation of gases into the trachea contaminates minute ventilation (VL), dead space volume (VD), tidal volume (VT), and other indices of gas exchange, as measured by usual technics. We overcame this problem by devising special methods of measuring inspired and expired ventilation, alveolar and dead space ventilation, and VT and VD by using pneumotachographic timing of inspiration and expiration so that true inspired and expired ventilation were calculated. We studied 5 patients with chronic CO2 retention from either COPD, scoliosis, or muscular dystrophy (annual average PaCO2 = 45 to 75 mm Hg) during 75 min of AI with serial gas exchange and arterial blood gas measurements. AI at about 5 L/min of room air through the trachea in 5 patients reduced VL by 18% (from 7.91 to 6.48 L/min), VT by 25% (from 450 to 338 ml), and VD by 37% (from 223 to 141 ml), while not affecting PaCO2 (from 51.8 to 48.2 mm Hg) or PaO2 (from 65.1 to 63.4 mm Hg). In 2 patients, AI administered continuously for 4 to 12 months (as 30 to 50% O2) maintained PaCO2 as well as or better than breathing enriched O2 from a tracheal collar via an open tracheostomy.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of physical exertion on respiratory airflow and airway resistance in patients with chronic bronchitis]

In a group of 30 men aged 44-60 years with chronic bronchitis the effect of physical effort was assessed on the value of airways resistance and expired air flow. Physical effort was noted to increase the air flow and decreases airways resistance in most cases of chronic bronchitis. A significant negative correlation was demonstrated between the TGV value and the flow-volume value, and changes of air flow after effort in chronic bronchitis patients depended on the resting TGV value.

A new technique to demonstrate flow limitation in partial expiratory flow-volume curves in infants

Partial expiratory flow-volume (PEFV) curves in infants are generated by applying a compressive pressure over the chest wall with an inflatable jacket. This study addresses two issues: pressure transmission to and across the chest wall and whether flow limitation can be identified. Eleven infants sedated with chloral hydrate were studied. Pressure transmission to the chest wall, measured with neonatal blood pressure cuffs placed on the infant's body surface, was 72 +/- 4% of jacket pressure during compression maneuvers. The pressure transmission to the air spaces, determined by measuring airway pressure during a compression maneuver against an occluded airway, was 56 +/- 6% of jacket pressure. A significant amount of the applied pressure is therefore lost across both the jacket and chest wall. Rapid pressure oscillations (RPO) were superimposed on static jacket pressures while expiratory flow was measured. Absence of associated oscillations of flow measured at the mouth was taken to indicate that flow was independent of driving pressure and therefore limited. Flow limitation was demonstrable with the RPO technique in all infants for jacket pressures greater than 50 cmH2O; however, it was evident at jacket pressures less than 30 cmH2O jacket pressure in four infants with obstructive airway disease. The RPO technique is a useful adjunct to the compression maneuver utilized to generate PEFV curves in infants because it facilitates the recognition of expiratory flow limitation.

Alveolar pressure and airway resistance during maximal and submaximal respiratory efforts

A digital computing technique was used to extract continuous calculations of average alveolar pressure and airway resistance from body plethysmographic measurements during forced inspiratory and expiratory vital capacity maneuvers and tidal breathing in human subjects. Derived alveolar pressures were similar to those obtained using an interrupter technique (linear regression slope, 0.99 +/- 0.02; r = 0.98) and by comparison with esophageal pressure measurements. Studies in normal subjects revealed a characteristic pattern of increasing airway resistance throughout the expiratory phases of maximal and submaximal respiratory maneuvers, with maximal resistance of 33 to 110 cm H2O/L/s at low lung volumes during forced vital capacities. In contrast, inspiratory resistance remained low and constant throughout maximal and submaximal inspiratory maneuvers. Patients with COPD showed substantially higher inspiratory and expiratory resistances. In three patients with flow-volume loops suggestive of variable extrathoracic upper airway obstruction, measurements of alveolar pressure and airway resistance made it clear that two of the patients had upper airway obstruction, whereas the other was exerting an inadequate effort. We conclude that this noninvasive technique provides valid estimates of alveolar pressure and airway resistance continuously throughout both phases of the respiratory cycle over a wide range of volumes and flow rates. It may prove to be useful in the assessment of effort and airway obstruction in patients with a variety of pulmonary conditions.

Increase in tracheal pressure during jet ventilation

Gas injection systems used in several techniques of ventilation cause increases in airway pressure and physiological changes which are frequently overlooked. The momentum flux theory describes such phenomena most appropriately. We have defined and measured the characteristics of such increases in airway pressure, using a lateral tracheal injection system which has been described previously. In such a system, wall friction is a major source of loss in jet momentum flux, in contrast with the changes in axis-symmetrical systems. This process results in a potentially beneficial increase in airway pressure and in greater mixing, which might be clinically useful.

Effects of air-flow limitation on the electrocardiogram in chronic obstructive pulmonary diseases (COPD)

Electrocardiographic studies have been carried out in one hundred and thirty patients of chronic obstructive pulmonary disease (COPD). The possible influence of air-flow limitation, alveolar air trapping, hypoxaemia and hypercapnia on the electrocardiographic findings indicative of right-sided cardiac involvement have been investigated. Thus, the findings: P greater than 2.5 mm, P-axis over +90 degrees, QRS axis over +90 degrees, RV6 less than or equal to 5mm and R/S ratio in V5 V6 less than or equal to 1.0 showed a significant negative correlation with FEV1/FVC ratio. The other features like Ta waves, negative P in AVL, S greater than 5 mm in depth in V5-6 and S1,S2,S3 pattern were observed to be less frequent and correlated weakly with the severity of the disease as judged by the lung function status. The reduction of FEV1/FVC was associated with increased residual volume (air trapping), hypoxaemia and hypercapnia. It is concluded that the ECG changes indicative of right-sided cardiac involvement may be produced by a combination of increased alveolar air trapping and blood gases derangement.

Computer simulation of respiratory impedance and flow transfer functions during high frequency oscillations

The usefulness of measuring respiratory flow in the airway and at the chest wall and of measuring respiratory input impedance (Z) to monitor high frequency ventilation was investigated by computer simulation using a monoalveolar 10-coefficient model. The latter included a central airway with its resistance (Rc) and inertance (lc), a resistive peripheral airway (Rp), a lumped bronchial compliance (Cb), alveolar gas compliance (Cgas), lung tissue with its resistance (RL) and compliance (CL), and chest wall resistance (RW), inertance (lw) and compliance (Cw). Gas flow in the peripheral airway (Vp), shunt flow through Cb (Vb), gas compression flow (Vgas) and rate of volume change of the lung (VL) and of the chest (VW) were computed and expressed as a function of gas flow in the central airway (Vc). For normal values of the coefficients, Vp/Vc was found to decrease moderately with increasing frequency and was still 0.75 at 20 Hz. Peripheral airway obstruction (Rp x 5) considerably decreased Vp/Vc, particularly at high frequency. It did not change the relationship between the two measurable flows, Vc and Vw, but increased the effective resistance at low frequency and shifted the reactance curve to the right. A reduced lung or chest wall compliance produced little change in Vp/Vc and Z except at very low frequencies; however, it decreased the phase lag between Vw and Vc. Finally, an increased airway wall compliance decreased Vp/Vc, but had little effect on Z and Vw/Vc. It is concluded that measuring respiratory impedance may help in detecting some, but not all of the conditions in which peripheral flow convection is decreased during high frequency oscillations.

A reinterpretation of psychologically induced airways changes

Psychologically induced airways changes in asthmatic individuals may be a function of variation in general activation level, not variation in asthma severity. The evidence for this hypothesis derives from work showing that healthy individuals exhibit psychologically induced airways changes similar to those exhibited by asthmatics. Individuals from both normal and healthy populations display increases in bronchomotor tone in response to stress and decreases in bronchomotor tone in response to relaxing stimulation. Although these responses are not limited to asthmatics, they are not irrelevant to asthma. Knowledge of specific relationships between airways changes and psychological factors is helpful in the management of asthma.

Responses of upper-airway dilating muscles and diaphragm activity to end-expiratory pressure loading in anesthetized dogs

The steady-state responses of upper-airway dilating muscles and diaphragm activity to elevation of lung volume induced by positive end-expiratory pressure loading were studied in 9 pentobarbital-anesthetized dogs with vagus nerves intact. The early and late effects of 5 min of expiratory threshold loads upon upper airway dilating muscle activity (the alae nasi, the genioglossus and the posterior cricoarytenoid) were compared to their effects on diaphragm activity. During resting O2 breathing, application of 5 and 10 cm H2O of positive end-expiratory pressure produced no significant change in the peak electrical activity of the upper-airway dilating muscles and diaphragm (p greater than 0.05). No qualitative differences were found in the upper-airway dilating muscles and diaphragm responses to expiratory threshold loads when the animals breathed 3 or 7% CO2 in O2, compared to when they inspired 100% O2. Furthermore, no differences were found in the electrical activity of the upper-airway dilating muscles and diaphragm at any given end-tidal CO2 when unloaded responses were compared with loaded responses during progressive hypercapnia. However, positive end-expiratory pressure loading caused significant prolongation of expiratory duration, which gradually returned toward control levels when the loads were maintained. In animals who developed periodic breathing by increasing levels of anesthesia, positive end-expiratory pressure loading eliminated the periodicity and made the pattern of breathing regular. Based on these results, it can be concluded that under the conditions of these experiments, increases in lung volume produced by expiratory threshold loads do not reduce the activity of upper-airway dilating muscles. The maintenance of the electrical activity of the upper-airway dilating muscles might be caused by excitatory reflex mechanisms or central habituation.

Effects of prolonged physical training on ventilatory response to hypercapnia

In order to determine whether or not resting ventilatory response to hypercapnia is changed by physical training, we studied the effect of long-term physical training on the slope of ventilatory response to CO2 at rest. The subjects were 9 untrained freshmen ranging in age from 18 to 20 years. Five out of nine subjects belonged to the badminton team after entering university in April 1980, and participated in their team's training for about 3 hr per day, 3 times a week year round for about 4 years until March 1984. Maximum oxygen uptake (VO2max), maximum pulmonary ventilation (VEmax) and maximum heart rate (HR max) were determined during maximal treadmill exercise before and after training. The slope (S) of ventilatory response to carbon dioxide at rest was measured by Read's rebreathing method. VO2max increased after training in the trained subjects and mean values of VO2max which were measured in 1982, 1983, and 1984, were statistically higher than that of 1980. Similar tendency was observed in VEmax and VO2max/W. Average values and standard deviations of S before training were 1.91 +/- 0.52 liter/min/torr and were decreased gradually with increasing training period; the differences in the S value before (1980) and after training, i.e., 1982, 1983, and 1984, were all significant. Such difference could still be seen after S was recalculated as SN by using normalized ventilation for 70 kg body weight, while there were no significant differences in the S and SN between baseline and repeated studies in the untrained group. In addition, CO2 responsiveness was found to correlate negatively with maximum oxygen uptake in 4 out of the 5 trained subjects. These results suggest that in normal subjects, long-term physical training, as in the present study, decreases CO2 responsiveness at rest.

Home sleep monitor for detecting apnea episodes by nasal flow and tracheal sound recordings

We have developed a portable home sleep monitoring system using nasal airflow (NA), tracheal sound recordings (TSR), and electrocardiogram (ECG). NA was recorded by two thermisters. TSR was recorded by a microphone attached to the skin overlying the cervical trachea. Three kinds of signals were recorded with a cassette recorder. Thirty-seven outpatients who had sleep complaints were monitored during sleep at home using this recorder. Attachment of the pickups was performed by the patients themselves. Recordings were played back and analyzed by a personal computer to evaluate apnea episodes from TSR and R-R intervals beat by beat. This home monitoring system had labor-saving and cost-saving benefits and seemed to be a satisfactory technique for screening.

Acid-Base Relationships in the Blood of the Toad, Bufo Marinus: II. The Effects of Dehydration

Cutaneous CO2 excretion is reduced as the skin dries during dehydration but an increase in breath frequency acts to regulate the arterial blood Pcoco2 and thus pHα. Moreover, the toad does not urinate and water is reabsorbed from the bladder to replace that lost by evaporation at the skin and lung surfaces. The animal does, however, produce a very acid bladder urine to conserve circulating levels of plasma [HCO3-] and this together with an increased ventilation effectively maintains the blood acid-base status for up to 48 h of dehydration in air. Water loss and acid production are presumably also reduced by the animal's behaviour; animals remain still, in a crouched position or in a pile if left in groups.

Dehydrated toads are less able than hydrated toads to regulate blood pH during hypercapnia: they hyperventilate and mobilize body bicarbonate stores in much the same fashion as hydrated animals but due to the restrictions on cutaneous CO2 excretion and renal output, there is comparatively little reduction in the PCOCO2 difference between arterial blood and inspired gas thereby resulting in a more severe respiratory acidosis. These factors further contribute to the persistent acidosis which continues even when the animals are returned to air.

Acid-Base Relationships in the Blood of the Toad, Bufo Marinus: I. The Effects of Environmental CO2

An abrupt increase in ambient CO2, resulted in a marked respiratory acidosis which took place within 30 min. During this time there was a considerable reduction in the PCO2. difference between arterial blood and inspired gas caused by an increase in ventilations. Prolonged CO2 exposure (24 h) showed that there was some compensation for the acidosis in that plasma bicarbonate concentrations increased substantially. At the same time, however, the PCO2 of arterial blood always rose so that the net result was usually only a small increase in pH. Upon return to air, the blood was backtitrated along a buffer line elevated above and parallel to that seen during the initial response to hypercapnia. The fall in arterial blood PCO2, during the early stages of recovery often led to pH values higher than those seen in the untreated animal. After 48 h in air, recovery had gone further with PCO2 pH and [HCO3-] levels approaching but rarely reaching the pre-exposure values.

Acid-Base Relationships in the Blood of the Toad, Bufo Marinus: III. The Effects of Burrowing

When Bufo marinus burrows, the skin becomes intimately surrounded by substrate but the nares always remain exposed to the surface air. Upon entering into a state of dormancy the animal hypoventilates and this together with the loss of the skin as a respiratory site results in a rise in arterial blood Pcoco2 despite a probable decline in metabolism. Even though lung ventilation falls, the toad regulates blood pH and the respiratory acidosis is progressively compensated for by a progressive increase in plasma [HCO3-] along the course of an elevated PCOCO2 isopleth. At steady state, the acidosis is fully compensated for by a new equilibrium ratio of HCO3- to PCOCO2 at the same pH as the non-burrowed animal. Arousal from the dormant state at this time results in a marked lung hyperventilation and a sharp decline in body CO2 stores