Respiratory inhibition with sympathetic afferent stimulation in the canine and primate

Regulation of breathing by cardiopulmonary afferents

This chapter broadly reviews cardiopulmonary sympathetic and vagal sensors and their reflex functions during physiologic and pathophysiologic processes. Mechanosensory operating mechanisms, including their central projections, are described under multiple sensor theory. In addition, ways to interpret evidence surrounding several controversial issues are provided, with detailed reasoning on how conclusions are derived. Cardiopulmonary sensory roles in breathing control and the development of symptoms and signs and pathophysiologic processes in cardiopulmonary diseases (such as cough and neuroimmune interaction) also are discussed.

Sensory nerves in lung and airways

Sensory nerves innervating the lung and airways play an important role in regulating various cardiopulmonary functions and maintaining homeostasis under both healthy and disease conditions. Their activities conducted by both vagal and sympathetic afferents are also responsible for eliciting important defense reflexes that protect the lung and body from potential health-hazardous effects of airborne particulates and chemical irritants. This article reviews the morphology, transduction properties, reflex functions, and respiratory sensations of these receptors, focusing primarily on recent findings derived from using new technologies such as neural immunochemistry, isolated airway-nerve preparation, cultured airway neurons, patch-clamp electrophysiology, transgenic mice, and other cellular and molecular approaches. Studies of the signal transduction of mechanosensitive afferents have revealed a new concept of sensory unit and cellular mechanism of activation, and identified additional types of sensory receptors in the lung. Chemosensitive properties of these lung afferents are further characterized by the expression of specific ligand-gated ion channels on nerve terminals, ganglion origin, and responses to the action of various inflammatory cells, mediators, and cytokines during acute and chronic airway inflammation and injuries. Increasing interest and extensive investigations have been focused on uncovering the mechanisms underlying hypersensitivity of these airway afferents, and their role in the manifestation of various symptoms under pathophysiological conditions. Several important and challenging questions regarding these sensory nerves are discussed. Searching for these answers will be a critical step in developing the translational research and effective treatments of airway diseases.

[Epidural analgesia apart from obstetrics: a survey of practice]

OBJECTIVES

To describe the current use of epidural anesthesia (EA) apart from obstetrics, and to explain the reasons of its low utilization.

STUDY DESIGN

Observational study.

METHODS

A survey of practice with a self-questionnaire was sent by e-mail and available on Internet. Answers were compared between groups doing or not an epidural analgesia with exact Fisher tests (P<0.05 statistically significant).

RESULTS

Among the 176 anesthesiologists who answered to the questionnaire, only 21.4% never used epidural analgesia. The main reasons were alternatives therapeutics such as PCA with opioids or TAP block (24/38 vs. 46/140). TAP block was the most common alternative used by more than 50% of anesthesiologists. Loss of competence (4/30 vs. 0/39) was rarely the reason to its low utilization. The low accessibility to specialized postoperative units was recognized in both groups as a limiting factor to do an epidural but not the fear of neurological complications. Those who never perform epidural analgesia were statistically more often physicians between 40 and 50 years (12/38 vs. 19/140). Heparin, aspirin and clopidogrel are no longer contraindications according to anesthesiologists less than 40 years old (50/68 vs. 31/68; 44/68 vs. 31/68; 37/68 vs. 23/68 respectively) but not for older.

CONCLUSIONS

Epidural analgesia is performed more often by younger anesthesiologists. This survey suggests the need of specific postoperative area to allow anesthesiologist to perform and supervise safely this technique. Recommendations of the French society of Anesthesiologists are also poorly applied.

Control of breathing during exercise

During exercise by healthy mammals, alveolar ventilation and alveolar-capillary diffusion increase in proportion to the increase in metabolic rate to prevent PaCO2 from increasing and PaO2 from decreasing. There is no known mechanism capable of directly sensing the rate of gas exchange in the muscles or the lungs; thus, for over a century there has been intense interest in elucidating how respiratory neurons adjust their output to variables which can not be directly monitored. Several hypotheses have been tested and supportive data were obtained, but for each hypothesis, there are contradictory data or reasons to question the validity of each hypothesis. Herein, we report a critique of the major hypotheses which has led to the following conclusions. First, a single stimulus or combination of stimuli that convincingly and entirely explains the hyperpnea has not been identified. Second, the coupling of the hyperpnea to metabolic rate is not causal but is due to of these variables each resulting from a common factor which link the circulatory and ventilatory responses to exercise. Third, stimuli postulated to act at pulmonary or cardiac receptors or carotid and intracranial chemoreceptors are not primary mediators of the hyperpnea. Fourth, stimuli originating in exercising limbs and conveyed to the brain by spinal afferents contribute to the exercise hyperpnea. Fifth, the hyperventilation during heavy exercise is not primarily due to lactacidosis stimulation of carotid chemoreceptors. Finally, since volitional exercise requires activation of the CNS, neural feed-forward (central command) mediation of the exercise hyperpnea seems intuitive and is supported by data from several studies. However, there is no compelling evidence to accept this concept as an indisputable fact.

Gallbladder bed irrigation with bupivacaine improves pulmonary functions after laparoscopic cholecystectomy

PURPOSE

Afferent stimulus arising from gallbladder and its bed may elicit reflex inhibition of the diaphragm. Pulmonary function would be improved by blocking this stimulus after laparoscopic cholecystectomy. This randomized prospective study evaluated this hypothesis in patients who underwent laparoscopic cholecystectomy.

MATERIALS AND METHODS

During the study period, 30 patients who underwent laparoscopic cholecystectomy were randomly divided into three groups. Group I: Laparoscopic cholecystectomy; Group II: Laparoscopic cholecystectomy + irrigation of gallbladder bed with 20 mL 0.5% bupivacaine solution; Group III: Laparoscopic cholecystectomy + irrigation of gallbladder bed with bupivacaine + 10 mL 0.5% bupivacaine solution was given via a catheter every 6 h. Pulmonary function tests were performed on the day before the operation and in the morning of the first postoperative day. Forced vital capacity (FVC), forced expiratory volume at 1 s (FEV-1), and forced expiratory flow at 25% to 75% (FEF 25-75%) were obtained.

RESULTS

Postoperative FVC measured 53.3 +/- 4.5% of preoperative function for group I, 70.8 +/- 5.7% for group II, and 68.8 +/- 4.7% for group III (p < 0.05). Postoperative FEV-1 measured 52.8 +/- 5.3% of preoperative function for group I, 69.7 +/- 4.9% for group II, and 70.5 +/- 5% for group III (p < 0.05). Postoperative FEF 25-75% measured 61.1 +/- 4.6% of the preoperative function for group I, 73.6 +/- 3% for group II, and 72.1 +/- 6% for group III (p < 0.05).

CONCLUSION

The results from this study indicated that considerable improvement of pulmonary function was acquired by gallbladder bed irrigation with bupivacaine after laparoscopic cholecystectomy.

Aspectos históricos da pressão arterial de oxigênio e espirometria relacionados à operação abdominal

INTRODUÇÃO: Operações, principalmente de abdome superior, cursam no pós-operatório com hipoxemia e distúrbios ventilatórios restritivos. O objetivos da presente revisão foram: a) fazer retrospecto histórico das técnicas espirométricas e da avaliação laboratorial da hipoxemia, por meio da pressão arterial de oxigênio (PaO2) e, b) rever os principais fatores responsáveis pelas alterações da função pulmonar pós-operatória. MÉTODOS: Fez-se revisão histórica sobre os principais aspectos espirométricos e da medida da PaO2, correlacionando esses exames como aferidores da função pulmonar, após operações abdominais. CONCLUSÕES: Operações em andar superior do abdome podem cursar com hipoxemia e distúrbios ventilatórios restritivos, cuja principal causa é a disfunção diafragmática, que pode ser minimizada por meio de laparoscopia e um eficaz tratamento da dor pós-operatória.

Decline of neuroadrenergic bronchial innervation and respiratory function in type 1 diabetes mellitus: a longitudinal study

BACKGROUND AND AIM

Type 1 diabetes mellitus complicated by autonomic neuropathy (AN) is characterized by depressed cholinergic bronchomotor tone and neuroadrenergic denervation of the lung. We explored the effects of AN on the rate of decline of pulmonary sympathetic innervation and respiratory function during a 5-year follow-up.

METHODS

Twenty diabetic patients, 11 with AN, were enrolled in 1998 and then followed-up until 2003. During follow-up, glycosylated haemoglobin (HbA1c) was measured every 3 months. In 1998 and 2003 the patients underwent respiratory function tests and a ventilatory scintigraphic study of neuroadrenergic bronchial innervation using 123I-MIBG.

RESULTS

During follow-up 4 patients, all with AN, were lost, and 1 developed AN. Forced vital capacity (FVC), and diffusing capacity of the lung for carbon monoxide (DLCO) showed comparable rates of decrease in patients with and without AN. The yearly decline of forced expiratory volume in 1 s (FEV1) was about double the physiologic rate, in both AN and AN-free patients. The MIBG clearance significantly increased both in patients with AN (T1/2: 118.88 +/- 30.14 min at baseline and 92.10 +/- 24.52 min at the end of follow-up) and without AN (135.14 +/- 17.09 min and 92.68 +/- 13.52 min, respectively), indicating a rapidly progressive neuroadrenergic denervation. The rate of the neuroadrenergic denervation was inversely related to the severity of autonomic dysfunction at baseline (Spearman's rho - 0.62, p = 0.017). Neither respiratory function indexes nor MIBG clearance changes correlated with the overall HbA1c values.

CONCLUSIONS

Neuroadrenergic denervation of the lung parallels the decline of respiratory function indexes in diabetic patients both with and without AN and seems to be independent from the quality of glycemic control.

Reflex regulation of airway sympathetic nerves in guinea-pigs

Sympathetic nerves innervate the airways of most species but their reflex regulation has been essentially unstudied. Here we demonstrate sympathetic nerve-mediated reflex relaxation of airway smooth muscle measured in situ in the guinea-pig trachea. Retrograde tracing, immunohistochemistry and electrophysiological analysis identified a population of substance P-containing capsaicin-sensitive spinal afferent neurones in the upper thoracic (T1-T4) dorsal root ganglia (DRG) that innervate the airways and lung. After bilateral vagotomy, atropine pretreatment and pre-contraction of the trachealis with histamine, nebulized capsaicin (10-60 microm) evoked a 63+/-7% reversal of the histamine-induced contraction of the trachealis. Either the beta-adrenoceptor antagonist propranolol (2 microm, administered directly to the trachea) or bilateral sympathetic nerve denervation of the trachea essentially abolished these reflexes (10+/-9% and 6+/-4% relaxations, respectively), suggesting that they were mediated primarily, if not exclusively, by sympathetic adrenergic nerve activation. Cutting the upper thoracic dorsal roots carrying the central processes of airway spinal afferents also markedly blocked the relaxations (9+/-5% relaxation). Comparable inhibitory effects were observed following intravenous pretreatment with neurokinin receptor antagonists (3+/-7% relaxations). These reflexes were not accompanied by consistent changes in heart rate or blood pressure. By contrast, stimulating the rostral cut ends of the cervical vagus nerves also evoked a sympathetic adrenergic nerve-mediated relaxation that were accompanied by marked alterations in blood pressure. The results indicate that the capsaicin-induced reflex-mediated relaxation of airway smooth muscle following vagotomy is mediated by sequential activation of tachykinin-containing spinal afferent and sympathetic efferent nerves innervating airways. This sympathetic nerve-mediated response may serve to oppose airway contraction induced by parasympathetic nerve activation in the airways.

Bradykinin B2 receptors mediate pulmonary sympathetic afferents induced reflexes in rabbits

Endogenous bradykinin (BK) is an established mediator of pulmonary inflammation, yet its role in lung disease is unclear. In the rabbit, injecting BK into the lung parenchyma elicits reflex hyperpnea, tachypnea, hypotension, and bradycardia by stimulating pulmonary sympathetic afferents. To further explore bradykinin effects, breathing pattern (phrenic nerve and abdominal muscle activities) and hemodynamics (blood pressure and heart rate) were examined in anesthetized, open-chest, and mechanically ventilated rabbits. Three receptor agonists [bradykinin, selective B(1) (des-Arg(9)-BK), and selective B(2) (Tyr(8)-BK)], as well as three B(2) receptor antagonists, B6029 (N alpha-Adamantaneacetyl)-Bradykinin, B(1)650 (D-Arg-[Hyp(3), Thi(5,8), D-Phe(7)]-Bradykinin, or Hoe-140 (D-Arg-[Hyp(3), Thi(5), D-Tic(7), Oic(8)] bradykinin), were used to identify the responsible receptor subtype. In both intact and vagotomized rabbits, injecting BK or a selective B(2) agonist into the lung elicited similar cardiopulmonary responses. These reflex responses were greatly attenuated or blocked by pre-injecting B(2) antagonists into the right atrium or into the lung parenchyma. In contrast, the B(1) agonist elicited fewer cardiopulmonary effects in intact rabbits and had no effect in vagotomized rabbits. We conclude that BK stimulates pulmonary sympathetic afferents [Soukhova, G., Wang, Y., Ahmed, M., Walker, J., Yu, J., 2003. Bradykinin stimulates respiratory drive by activating pulmonary sympathetic afferents in the rabbit. J. Appl. Physiol. 95, 241-249.; Wang, Y., Soukhova, G., Proctor, M., Walker, J., Yu, J., 2003. Bradykinin causes hypotension by activating pulmonary sympathetic afferents in the rabbit. J. Appl. Physiol. 95, 233-240.], eliciting a characteristic cardiopulmonary reflex via B(2) receptors.

Bradykinin causes hypotension by activating pulmonary sympathetic afferents in the rabbit

Bradykinin (BK) activates sympathetic afferents in the heart, intestine, and kidney, and it alters hemodynamics. However, we know little about the influence of pulmonary sympathetic afferents on circulation. Activation of pulmonary afferents by directly injecting stimulants into the lung parenchyma permits examination of reflexes that originate in the lung without confounding effects from the systemic circulation. In the present study, we tested the hypothesis that pulmonary sympathetic afferents exert a significant influence on hemodynamics. We examined reflex effects of injecting BK (1 microg/kg in 0.1 ml) into the lung parenchyma on circulation in anesthetized, open-chest, artificially ventilated rabbits. BK significantly decreased mean arterial blood pressure (BP) (27 +/- 3 mmHg) and heart rate (19 +/- 4 beats/min). Both effects remained after bilateral vagotomy. To rule out possible direct systemic vasodilation by BK, we examined renal sympathetic nerve activity (RSNA) in response to BK injection and examined BP responses to injection of ACh (0.1 ml of 10-4 M). BK suppressed the RSNA before and after vagotomy. ACh did not change BP when injected into the lung parenchyma, but it decreased BP (31 +/- 3 mmHg) when injected into the right atrium. Our data indicate that activating pulmonary sympathetic afferents reflexly suppresses hemodynamics.

Bradykinin stimulates respiratory drive by activating pulmonary sympathetic afferents in the rabbit

We recently identified a vagally mediated excitatory lung reflex by injecting hypertonic saline into the lung parenchyma (Yu J, Zhang JF, and Fletcher EC. J Appl Physiol 85: 1485-1492, 1998). This reflex increased amplitude and burst rate of phrenic (inspiratory) nerve activity and suppressed external oblique abdominal (expiratory) muscle activity. In the present study, we tested the hypothesis that bradykinin may activate extravagal pathways to stimulate breathing by assessing its reflex effects on respiratory drive. Bradykinin (1 microg/kg in 0.1 ml) was injected into the lung parenchyma of anesthetized, open-chest and artificially ventilated rabbits. In most cases, bradykinin increased phrenic amplitude, phrenic burst rate, and expiratory muscle activity. However, a variety of breathing patterns resulted, ranging from hyperpnea and tachypnea to rapid shallow breathing and apnea. Bradykinin acts like hypertonic saline in producing hyperpnea and tachypnea, yet the two agents clearly differ. Bradykinin produced a higher ratio of phrenic amplitude to inspiratory time and had longer latency than hypertonic saline. Although attenuated, bradykinin-induced respiratory responses persisted after vagotomy. We conclude that bradykinin activates multiple afferent pathways in the lung; portions of its respiratory reflexes are extravagal and arise from sympathetic afferents.

Cutaneous sympathetic motor rhythms in the decerebrate rat

Investigation of rhythmic discharges may provide insights into integrative mechanisms underlying nervous system control of effectors. We have previously shown that, in CNS-intact, anesthetized rats, cutaneous sympathetic vasoconstrictor neurones innervating thermoregulatory circulations exhibit a robust rhythmicity in the 0.4-1.2-Hz frequency range (T-rhythm). Here we examined whether the neural circuitry required to generate this rhythm remained intact in decerebrate (at collicular level), paralyzed and artificially ventilated preparations with cervical vagotomy, ligation of common carotid arteries and pneumothorax. Population sympathetic activity was recorded from the ventral collector nerve (VCN) of the tail in nine animals, while monitoring central respiratory drive. We found that rhythmic activity remained a robust feature and that activity behaved in a comparable manner to that previously described in the intact anesthetized preparation. Manifest as peaks in the autospectra, the dominant rhythm was either at the frequency of (f) lung inflation cycle (fLIC), central respiratory drive (fCRD) or in the 'free-run' T-rhythm frequency range. Through manipulation of fLIC we could alter the dominant rhythm of discharges. We show a significant relationship between fLIC and the likelihood of the dominant rhythm in VCN discharges being at fLIC or at a frequency that was neither fLIC nor fCRD. At fLIC of 1 Hz: in seven of nine animals the VCN dominant rhythm was 1 Hz, zero of nine displayed a dominant T-rhythm; at fLIC of 2 Hz: two of nine had a dominant VCN rhythm at 2 Hz and five of nine a T-rhythm. Furthermore, CRD was never observed to entrain to fLIC. These experiments demonstrate that the network underlying the generation of the T-rhythm is located below the collicular level of the neuraxis and that in this preparation LIC-related modulation of discharges may be mediated by spinal (sympathetic) afferents.

Cerebrovascular reactivity and hypercapnic respiratory drive in diabetic autonomic neuropathy

Because abnormalities in cerebrovascular reactivity (CVR) in subjects with long-term diabetes could partly be ascribed to autonomic neuropathy and related to central chemosensitivity, CVR and the respiratory drive output during progressive hypercapnia were studied in 15 diabetic patients without (DAN-) and 30 with autonomic neuropathy (DAN+), of whom 15 had postural hypotension (PH) (DAN+PH+) and 15 did not (DAN+PH-), and in 15 control (C) subjects. During CO(2) rebreathing, changes in occlusion pressure and minute ventilation were assessed, and seven subjects in each group had simultaneous measurements of the middle cerebral artery mean blood velocity (MCAV) by transcranial Doppler. The respiratory output to CO(2) was greater in DAN+PH+ than in DAN+PH- and DAN- (P < 0.01), whereas a reduced chemosensitivity was found in DAN+PH- (P < 0.05 vs. C). MCAV increased linearly with the end-tidal PCO(2) (PET(CO(2))) in DAN+PH- but less than in C and DAN- (P < 0.01). In contrast, DAN+PH+ showed an exponential increment in MCAV with PET(CO(2)) mainly >55 Torr. Thus CVR was lower in DAN+ than in C at PET(CO(2)) <55 Torr (P < 0.01), whereas it was greater in DAN+PH+ than in DAN+PH- (P < 0.01) and DAN- (P < 0.05) at PET(CO(2)) >55 Torr. CVR and occlusion pressure during hypercapnia were correlated only in DAN+ (r = 0.91, P < 0.001). We conclude that, in diabetic patients with autonomic neuropathy, CVR to CO(2) is reduced or increased according to the severity of dysautonomy and intensity of stimulus and appears to modulate the hypercapnic respiratory drive.

Diaphragm movement before and after cholecystectomy: a sonographic study

Respiratory disorders after abdominal surgery are commonly explained by changes in diaphragmatic movement that are difficult to demonstrate and quantify. Our aim was thus to quantify these changes using a noninvasive method. We used M-mode sonography for the prospective study to measure diaphragmatic amplitude in 14 patients before and after cholecystectomy. During quiet breathing, the diaphragm inspiratory amplitude (DIA) was significantly decreased after surgery from 1.4 +/- 0.2 cm to 1 +/- 0.1 cm and from 1.6 +/- 0.3 cm to 1.2 +/- 0.3 cm in the Laparoscopic and Open Cholecystectomy groups, respectively. The total time cycle of diaphragmatic motion decreased significantly in the two groups. The DIA also decreased significantly during deep breathing after cholecystectomy from 6.0 +/- 0.8 cm to 3.0 +/- 1.8 cm and from 6.1 +/- 1.3 cm to 3.1 +/- 1.6 cm in the Laparoscopic and Open Cholecystectomy groups, respectively. The six patients who underwent spirometric examination showed, during quiet breathing, a significant decrease in DIA without change in tidal volume, i.e., 0.51 +/- 0.08 L to 0.45 +/- 0.08 L. We found a significant decrease in DIA after cholecystectomy and a significant interindividual correlation between DIA during deep inspiration and inspiratory capacity. Using M-mode sonography techniques, we were able to demonstrate changes in diaphragmatic mobility after laparoscopic or open cholecystectomy.

IMPLICATIONS

Cholecystectomy at times results in impaired respiratory and diaphragmatic functions. The techniques currently used to study these repercussions are both laborious and invasive. Our sonographic technique is completely noninvasive and can be used to study diaphragm morphology and movement in real time.

Effects of abdominal or cardiopulmonary sympathetic afferents on upper cervical inspiratory neurons

Responses of upper cervical inspiratory neurons (UCINs) to abdominal visceral or cardiopulmonary sympathetic stimulation were studied using extracellular recordings from 213 UCINs in 54 pentobarbital sodium-anesthetized and paralyzed rats. Phrenic nerve activity was used to assess inspiration. The UCINs discharging during inspiration only were mainly in the C(1) segment, whereas phase-spanning UCINs were mostly in the C(2) segment. Phase-spanning activity was typically retained after overventilation or vagotomy. When greater splanchnic nerve (GSN) or cardiopulmonary sympathetic afferent (CPSA) fibers were electrically stimulated, augmented UCIN activity was observed in 65% of cells responding to CPSA stimulation but in only 17% of cells responding to GSN. Response latencies were 10.7 +/- 0.5 and 20.6 +/- 1.5 (SE) ms, respectively. Many augmented responses to CPSA stimulation (64%) and all augmented responses to GSN stimulation were followed by suppression of UCIN discharge (biphasic response). Phrenic nerve activity was suppressed by both GSN and CPSA stimulation, but with shorter latency for the latter (29 +/- 0.7 vs. 14.0 +/- 0.7 ms). Excitation of UCINs using CPSA stimulation occurs more often and by a more direct pathway than for GSN input.

Stimulation of breathing by activation of pulmonary peripheral afferents in rabbits

Respiratory response to selective activation of vagal afferents in the peripheral airways was investigated in anesthetized, open-chest, and artificially ventilated rabbits. Phrenic activity was used as an index of central respiratory drive before and after injection of hypertonic saline (8.1%, 0.1 ml) into the periphery of the lung to stimulate the afferents. The amplitude of "integrated" phrenic activity and phrenic burst rate increased by 19 +/- 3.4 and 53.7 +/- 12.7% (n = 23; P < 0.001), respectively. The response peaked at 5.5 +/- 1.6 s and returned to the baseline at 7 min (median) after the injection. The magnitude of the response was positively related to the concentration of injected NaCl. The response could not be elicited by injection of normal saline and was abolished by vagotomy. Because artificial ventilation caused phrenic activity to be entrained with the ventilator, respiratory drive was further assessed after the ventilator was stopped. Again, neural hyperpnea and tachypnea were observed. Because activation of a small fraction of the pulmonary peripheral afferents resulted in vigorous stimulation of respiratory drive, we speculate that initiation of this reflex may contribute to hyperpnea and tachypnea under both physiological and pathophysiological conditions.

Influence of autonomic neuropathy of different severities on the hypercapnic drive to breathing in diabetic patients

To investigate the effects of the autonomic nervous system on control of breathing, the neuromuscular (mouth occlusion pressure at 0.1 s after onset of inspiration [P0.1]) and ventilatory (minute ventilation [VE]) response to progressive hyperoxic hypercapnia was assessed in diabetic patients with autonomic dysfunction of different severity. Eighteen diabetics with autonomic neuropathy, nine with parasympathetic damage (DANp), and nine with parasympathetic and sympathetic damage (DANp+s), as indicated by marked postural hypotension, low increment of diastolic BP during sustained handgrip, and lowest resting catecholamine plasma levels, were studied together with a group of 10 diabetic patients without autonomic neuropathy (D) and a group of 10 normal subjects (C). All subjects had pulmonary function tests, including maximal voluntary ventilation and diffusion of carbon monoxide, measurements of respiratory muscle strength as maximal inspiratory mouth pressure (MIP) and maximal expiratory mouth pressure (MEP), and a CO2 rebreathing test (Read's method). Although in the normal range, lung volumes and FEV1 and forced expiratory flows were lower in the DANp and DANp+s groups than in the D and C groups, MIP and MEP were similar among C and diabetic groups, as well as resting P0.1, VE, tidal volume (VT), and respiratory rate (RR). The slope of the linear relationship between P0.1 and end-tidal PCO2 (PETCO2) was higher in DANp+s (0.63+/-0.07 cm H2O/mm Hg) than in C (0.45+/-0.06 cm H2O/mm Hg; p<0.05) and three times greater in DANp+s than in D (0.26+/-0.03 cm H2O/mm Hg; p<0.001) and DANp (0.24+/-0.03 cm H2O/mm Hg; p<0.001), who in turn showed a lower deltaP0.1/deltaPETCO2 than C. The VE increase with increasing PETCO2 was greater in DANp+s (3.70+/-0.85 L/min/mm Hg) than in DANp (2.13+/-0.20 L/min/mm Hg; p<0.05) and D (2.37+/-0.40 L/min/mm Hg; p=0.07), but not significantly higher from that of C (3.17+/-0.36 L/min/mm Hg). No differences were found for deltaVT/deltaPETCO2 among the groups, whereas the deltaRR/deltaPETCO2 relationship was steeper in DANp+s than in DANp (p<0.05) and D (p=0.055). These data reflect a depressed CO2 response both in D and DANp. The presumable decrease of the sympathetic nerve traffic in DANp+s appears to reverse this abnormality. DANp+s, however, exhibit an enhanced CO2 neuromuscular response even in respect to C, suggesting that the sympathetic nervous system might modulate the output of the respiratory centers to hypercapnic stimulus.

Role of vagal lung C-fibres in the cardiorespiratory effects of capsaicin in monkeys

Apnoea, bradycardia and hypotension were elicited by right atrial injections of capsaicin in anaesthetized monkeys. At the threshold dose (2.5 +/- 0.3 microgram/kg), tachypnoea was elicited (latency 1.6 +/- 0.2 s) which got replaced by apnoea with higher doses of capsaicin. These responses persisted (1) after cooling the cervical vagi to 6-8 degrees C, and (2) after instilling xylocaine into the pericardial sac. Tachypnoea and apnoea were elicited after bilateral cervical vagotomy also, but only with higher doses and after a longer latency (5.0 +/- 0.3 s). Right atrial injection of capsaicin and insufflation of halothane stimulated vagal pulmonary C-fibre receptors with a latency of 1.7 +/- 0.7 s and 0.2 +/- 0.1 s, respectively. Tachypnoea/apnoea, bradycardia and hypotension were elicited by left atrial injection of capsaicin also (threshold dose: 5.0 +/- 1.2 micrograms/kg). The respiratory responses persisted (1) after instilling xylocaine into the pericardial sac, and (2) after bilateral cervical vagotomy suggesting that they were due to stimulation of non-cardiac receptors with sympathetic afferents. It is concluded that the initial respiratory responses elicited by right atrial injection of capsaicin were due to stimulation of pulmonary C-fibre receptors with vagal afferents.

Ventilatory response to exercise in diabetic subjects with autonomic neuropathy

We have used diabetic autonomic neuropathy as a model of chronic pulmonary denervation to study the ventilatory response to incremental exercise in 20 diabetic subjects, 10 with (Dan+) and 10 without (Dan-) autonomic dysfunction, and in 10 normal control subjects. Although both Dan+ and Dan- subjects achieved lower O2 consumption and CO2 production (VCO2) than control subjects at peak of exercise, they attained similar values of either minute ventilation (VE) or adjusted ventilation (VE/maximal voluntary ventilation). The increment of respiratory rate with increasing adjusted ventilation was much higher in Dan+ than in Dan- and control subjects (P < 0.05). The slope of the linear VE/VCO2 relationship was 0.032 +/- 0.002, 0.027 +/- 0.001 (P < 0.05), and 0.025 +/- 0.001 (P < 0.001) ml/min in Dan+, Dan-, and control subjects, respectively. Both neuromuscular and ventilatory outputs in relation to increasing VCO2 were progressively higher in Dan+ than in Dan- and control subjects. At peak of exercise, end-tidal PCO2 was much lower in Dan+ (35.9 +/- 1.6 Torr) than in Dan- (42.1 +/- 1.7 Torr; P < 0.02) and control (42.1 +/- 0.9 Torr; P < 0.005) subjects. We conclude that pulmonary autonomic denervation affects ventilatory response to stressful exercise by excessively increasing respiratory rate and alveolar ventilation. Reduced neural inhibitory modulation from sympathetic pulmonary afferents and/or increased chemosensitivity may be responsible for the higher inspiratory output.

Reflex effects of stimulation of sympathetic afferents on the triangularis sterni

The purpose of this study was to determine whether contralateral inhibition of the triangularis sterni is produced by stimulation of intrathoracic sympathetic afferents. Dogs were anesthetized with sodium pentobarbital and placed on positive pressure ventilation. The chest was opened through a mid-sternal incision. Diaphragm and left and right triangularis sterni EMGs were recorded, post-vagotomy, before and during electrical stimulation of the left ventral ansa subclavia (VA), vagosympathetic trunk, ventrolateral and ventromedial cardiac nerves and, when present, the stellate cardiac nerve. Peak of the phasic diaphragm EMG and expiratory time were not significantly affected by stimulation of the VA. A significant decrease in inspiratory time was observed. Ipsilateral excitation and contralateral inhibition of the left and right triangularis sterni EMGs, respectively, were produced by stimulation of the VA. Stimulation of the other intrathoracic nerves produced a similar pattern of results. Conduction velocity determinations suggested that the afferents which produced the reflex responses are, at least in part, small A fibers.

Computer-assisted neurovegetative monitoring in patients after heart transplantation

The effects of orthotopic heart transplantation on spontaneous fluctuations of the respiration rate and heart rate were studied with a computer-assisted system for neurovegetative monitoring in 22 patients (mean age +/- SD: 48.7 +/- 9.4 years) 19.5 +/- 14.4 months after transplantation. The control group consisted of 12 healthy volunteers (mean age +/- SD: 38.7 +/- 6.6 years). The mean (+/- SE) respiratory rate was higher in the transplantation group than in the control group (17.7 +/- 0.8/min vs. 14.6 +/- 1.1 breaths/min, P < 0.2). The mean variability of the respiratory rate was smaller in the transplant patients than in the controls (3.7 +/- 0.3 vs. 2.8 +/- 0.4, P < 0.2). The heart rate variability coefficient in the patients after transplantation was lower than that in the controls (1.3 +/- 0.1% vs. 6.9 +/- 0.5%, P < 0.001). Spectral analysis of heart rate variability showed a smaller decrease of variability of respiration (P < 0.05) than of blood pressure regulation (P < 0.001) or of the angiotensin-renin system (P < 0.001). A separate group of 7 transplant patients (mean age 51.0 +/- 7.7 years) had activated cardiac pacemakers and thus no spontaneous physiologic heart rate oscillations. The variability of the respiratory rate in these patients was lower than in the other 22 transplant patients (1.8 +/- 0.2 vs. 3.7 +/- 0.3, P < 0.001). The data provided by multiparametric neurovegetative monitoring support the evaluation of complex regulatory mechanisms of respiratory and cardiovascular function and their adaptability after orthotopic heart transplantation.

Persistent postoperative hiccups: a review

The pathogenesis of persistent postoperative hiccups is not known. Hiccups can present as a symptom of a subphrenic abscess of gastric distention, and metabolic alterations may also cause hiccups. The hiccups may develop because of increased activity in neural reflex pathways not yet fully defined. Numerous treatment modalities have been tried but with questionable success. Valproate has proven effective in two trials investigating persistent non-surgical hiccups. The simple application of a nasogastric tube may successfully treat the hiccups, possibly because of an alteration of the activity in the reflex neural pathways involved. The available literature on the treatment of persistent hiccups is reviewed, and a treatment protocol for persistent postoperative hiccups is provided.

Hypoxaemia and myocardial ischaemia during and after endoscopic cholangiopancreatography: call for further studies

Sixteen non-selected patients undergoing endoscopic cholangiopancreatography (ERCP) after diazepam premedication were monitored for oxygen saturation (SpO2) with a pulse oximeter and for myocardial ischaemia with a Holter tape recorder from 2 h before ERCP to 6 h after the procedure. One patient was excluded from data analysis because of oxygen therapy. Oxygen saturation was significantly decreased (p less than 0.05) both during endoscopy and in the postendoscopy recovery period. Heart rate was significantly increased (p less than 0.05) both during and after the procedure. ST depression occurred in no patients before endoscopy, in 10 patients during, and in no patients after endoscopy. Concurrent ischaemia and episodic hypoxaemia were found in 5 patients, isolated ischaemia in 7 patients, and isolated episodic hypoxaemia in 13 patients. Concurrent ischaemia and tachycardia were found in 10 patients, ischaemia without tachycardia in no patients, and isolated tachycardia in 1 patient. There was no significant correlation between diazepam dose and SpO2 during endoscopy. These results suggest tachycardia to be more important than hypoxaemia in the pathogenesis of myocardial ischaemia during upper gastrointestinal endoscopy. Cardioprotective measures other than oxygen therapy should soon be evaluated before the implications of the new standards of care in endoscopy have become generally adopted.

Reflex ventilatory effects of KCl stimulation of lung receptors with sympathetic afferents

The purpose of this study was to determine the reflex ventilatory effects produced by lung receptors with sympathetic afferent nerves. Seven dogs were anesthetized with sodium pentobarbital, placed on a ventilator, and vagotomized. The chest was opened through a mid-sternal incision. Diaphragm EMG (D-EMG), right and left triangularis sterni EMG (TS-EMG), systemic arterial blood pressure (BP), and tracheal pressure were recorded before and after the application of 2 M KCl to the right or left lung near the venous hilum. The reflex effects produced by KCl applied to the superior vena cava (SVC) and of mechanical distortion of the lungs were also studied. KCl applied to the right or left lung or right or left lung distortion produced significant increases in peak TS-EMG ipsilateral to the applied stimulus with no significant effects on the contralateral TS-EMG. BP, inspiratory time, expiratory time, or peak D-EMG were not significantly affected, except for a decrease in inspiratory time when KCl was applied to the left lung and a decrease in BP with distortion of the left lung. KCl applied to the SVC produced a significant reflex increase in the right TS-EMG. The primary reflex response to chemical stimulation of lung receptors with sympathetic afferents was an increase in expiratory muscle activity. Additionally, mechanical stimulation may also activate these receptors. Furthermore, receptors which produce similar reflex responses are located on the SVC. That the reflex responses produced by intrathoracic receptors with sympathetic afferents were unilateral suggests that spinal mechanisms are involved.

Pulmonary denervation in humans. Effects on dyspnea and ventilatory pattern during exercise

The role of the pulmonary autonomic nerves in the mediation of respiratory sensation is unclear. Pulmonary neurogenic mechanisms may contribute to dyspnea either directly or indirectly via an influence on the pattern of ventilation. Using human heart-lung transplantation as a model of pulmonary denervation, we studied the ventilatory response, respiratory drive (P0.1), and sensation of breathlessness (modified Borg scale) during maximal incremental bicycle exercise. The subjects were four female heart-lung transplant recipients 3 to 9 months post-transplant and 10 age-matched control subjects. The ventilatory response to increasing CO2 output (VCO2) was higher (p less than 0.001) in transplant recipients than in control subjects, such that ventilation at peak exercise was similar in the two groups despite a lower peak VCO2 in transplant recipients. The ratio of tidal volume to inspiratory capacity increased with increasing ventilation in a similar fashion in both groups. Although the respiratory rate increased more quickly in transplant recipients, it was similar at peak ventilation in the two groups. Ventilatory timing and duty cycle at half-peak and peak ventilation were similar in transplant recipients and control subjects. Dyspnea ratings were not different between the two groups at similar levels of ventilation. Dyspnea as a function of P0.1 was also similar in transplant and control groups. These results indicate that pulmonary neurogenic mechanisms play a role in determining the level, but not the pattern, of ventilation during exercise. Furthermore, these pathways do not appear to contribute significantly to the perception of breathlessness in normal humans.

Respiratory changes induced by activation of testicular afferents in dogs

Reportedly, more than 90% of the testicular afferents of the dog are of the polymodal type. The possible involvement of these afferents in modulation of respiration was studied using anesthetized dogs, which had been vagotomized and with both common carotid arteries ligated. Electrical stimulation of the superior spermatic nerve at an intensity of 1/5 Tc (Tc: threshold intensity for C-fiber activation) induced no substantial changes in respiration, while above 1/2 Tc it induced an increase in minute expiratory volume (VE), or a decrease followed by an increase in VE. The pattern of respiratory change was converted from the former to the latter by increasing the stimulation frequency while maintaining the same intensity. Mechanical stimulation of the testis through a stimulator with a tip of 1 cm in diameter caused an increase of VE at 200 g and a decrease followed by an increase of VE above 500 g. Intra-arterial injection of bradykinin (3 x 10(-6) M), hypertonic saline (1.5 M) and high K+ solution (180 mM) to the spermatic artery induced similar respiratory changes. Pneumograms showed a shift in end-expiratory position even at stimulus intensities without significant VE changes. Phrenic nerve recordings from some artificially ventilated dogs, revealed an prolongation of the first expiratory phase followed by augmentation of phrenic activity, mostly an increase in respiratory rate. Comparison between afferent activities and reflex respiratory changes suggests that above described two types of respiratory changes are brought about by the activities of testicular polymodal receptors.

Respiratory responses to chemical activation of left ventricular receptors

Respiratory responses to chemical activation of receptors in the left ventricle were measured in anesthetized cats. Application of capsaicin (10 micrograms) or bradykinin (500 ng) to the serosal surface of the left ventricle caused increases in phrenic nerve activity and in arterial pressure. These responses persisted after cervical vagotomy and after bilateral transection of the carotid sinus nerves. Bilateral stellate ganglionectomy abolished the respiratory responses to capsaicin and bradykinin. In addition, stellate ganglionectomy prevented the arterial pressure response to bradykinin; however, a slight increase in arterial pressure occurred with application of capsaicin. It is concluded that activation of sympathetic afferents originating in the left ventricle causes an increase in respiratory output.

Responses of upper airway, intercostal and diaphragm muscle activity to stimulation of oesophageal afferents in dogs

The effects of oesophageal distension on respiratory patterns and the moving average electromyogram (e.m.g.) activity of three upper airway muscles--the alae nasi, the genioglossus, and the posterior cricoarytenoid--and four chest wall muscles--the costal and crural diaphragm and the inspiratory and expiratory intercostals--were examined in ten anaesthetized, tracheostomized, spontaneously breathing dogs. Distension was produced by inflations of a balloon placed in the middle part of the thoracic oesophagus with volumes of air ranging from 50 to 200 ml. Oesophageal distension increased respiratory frequency, mainly due to a significant shortening of the expiratory time. Activity of both the costal and crural parts of the diaphragm was inhibited with oesophageal distension, whereas that of the inspiratory intercostal muscles increased, tending to maintain a near-normal tidal volume and end-tidal CO2. Phasic inspiratory activity of all three upper airway muscles increased in response to oesophageal distension, as did the activity of the expiratory intercostal muscles. The changes in the breathing pattern and the electrical activity of all muscles in response to oesophageal distension were immediate, occurring during the first breath after the balloon was inflated. The responses were graded, so that increases in the volume of the oesophageal balloon progressively increased the activity of the upper airway and intercostal muscles, and decreased diaphragm activity. Bilateral vagotomy abolished the effects of oesophageal distension on upper airway and chest wall muscle activity, suggesting that vagal afferents constitute the major pathway for the reflex.

Rapid shallow breathing evoked by selective stimulation of airway C fibres in dogs

1. We have examined the reflex changes in breathing evoked in anaesthetized dogs by stimulation of the afferent vagal C fibres that supply the intrapulmonary and lower extrapulmonary airways. We stimulated bronchial (intrapulmonary) C fibres selectively by injecting bradykinin into the right bronchial artery (the chest had been opened briefly for insertion of a bronchial arterial catheter).2. Bronchial arterial injection of bradykinin (0.15-1.5 mug in 3-6 sec) usually caused a brief bout of rapid shallow breathing, which was sometimes preceded by apnoea. Infusion of bradykinin (0.2-2.0 mug min(-1) for 2-12 min) caused prolonged rapid shallow breathing, the breathing frequency (f) increasing by 19-102% and tidal volume (V(T)) decreasing by 13-87%; end-tidal P(CO2) decreased by 2-9 mmHg in several experiments. Rapid shallow breathing was also evoked by administration of bradykinin aerosol through a lower tracheal cannula.3. Cutting the vagus nerves or cooling them to 0 degrees C abolished the prolonged rapid shallow breathing evoked by bradykinin, but intermittent disturbances of breathing could still be elicited in some dogs. These residual effects often consisted of irregular spasmodic inspirations, which were abolished by avulsion of the right upper thoracic sympathetic chain.4. Rapid shallow breathing was accompanied by contraction of airway smooth muscle in an innervated segment of the upper trachea; contraction was abolished by cutting or cooling the vagus nerves.5. Arterial blood pressure often decreased briefly when bradykinin was injected into the bronchial artery; changes in pressure were smaller and less frequent when bradykinin was infused slowly, and pressure was usually unaltered when bradykinin was administered as an aerosol. Rapid shallow breathing occurred whether pressure decreased, increased or was unchanged. A number of other observations indicated that the changes in breathing were independent of the changes in blood pressure. Changes in heart rate were complex and appeared to result from the interplay of several reflexes. Marked cardiac slowing was evoked by bradykinin aerosol.6. Bradykinin injected into a bronchial artery is known to stimulate bronchial (intrapulmonary) C fibres. Results of recording afferent vagal impulses in the present study indicated that bradykinin administered as an aerosol stimulated bronchial C fibres and also C fibres with endings in the lower trachea and extrapulmonary bronchi. Irritant and pulmonary stretch receptors were not stimulated unless aerosols were administered repeatedly and in higher concentration. Hence airway C fibres appeared to be responsible for the reflex effects of bradykinin aerosol.7. Bronchial C fibres are stimulated by substances (bradykinin, prostaglandins and histamine) known to be released by the lungs and airways in a variety of pathophysiological circumstances. Results of this and previous studies are compatible with the hypothesis that stimulation of bronchial C fibres plays a major role in evoking the rapid shallow breathing, bronchoconstriction and increased secretion by airway submucosal glands that are part of the pulmonary defence response.

Effects of chronic lung denervation on breathing pattern and respiratory gas exchanges during hypoxia, hypercapnia and exercise

The influence of vagal fibres from the lung on ventilatory responses to hypercapnia, hypoxia and exercise was studied in two intact dogs (C) and two chronically lung denervated dogs (C.L.D.). In intact dogs, inspiration duration did not change as tidal volume increased in response to increased chemical drives. Chronic lung denervation did not affect the hypercapnia- or hypoxia-induced elevations in V, despite significant changes in breathing pattern. During exercise, oxygen consumption was similar for C and C.L.D. animals. V for a given oxygen uptake was the same in C and C.L.D. dogs, but VT was higher in C.L.D. animals at all levels of exercise. It is concluded that vagal fibres from the lung play a role in determining the breathing pattern, but are not required for a normal ventilatory response to hypercapnia, hypoxia and exercise. Interaction between vagal sensory input and specific structures sensitive to chemical or physical stimuli is discussed.

Time course of intercostal afferent termination of the inspiratory process

The influence exerted by several somatic nerves on the inspiratory off-switch mechanism has been assessed in decerebrate cats. These animals were paralyzed, artificially ventilated, and bilaterally vagotomized. Inspiratory activity was monitored by a phrenic neurogram. Brief stimulation of either the superficial radical nerve or the sciatic nerve had an inconsistent effect on both the depth of inspiration and the timing of the respiratory cycle. However, stimulation of the T6 intercostal nerve during inspiration elicited a premature phase switch to expiration. Distinct, repeatable thresholds were determined for 10 delays in 100 msec increments after the onset of inspiration. As the delay increased, the threshold current was observed to decrease in all 30 decerebrate cats studied. An increase in the end-expiratory %CO2 caused an elevation of the stimulus threshold. These results correspond to the known characteristics of the inspiratory off-switch. Also, since the intercostal afferents are not normally a major determinant of respiratory rhythmicity in eupnea, this work establishes intercostal nerve stimulation as a very useful technique in the study of inspiratory to expiratory phase switching mechanisms.

Sleep state effects on breathing after spinal cord transection and vagotomy in the cat

The role of chest wall and vagal afferents on breathing during wakefulness (W), nonrapid eye movement sleep (NREM), and REM sleep was assessed in 16 adult cats implanted with electrodes and skull bolts for sleep recordings with head restraint. Breathing was monitored with a pneumotachograph. Following control recordings establishing characteristic respiratory patterns during each state, cats sustained spinal cord transections at T-1, vagotomies, or both. The transections decreased variability of breathing rate, while vagotomies decreased rate but increased variability and tidal volume. These deafferentations alone or in combination failed to eliminate the major effects of state upon breathing pattern. Different states of consciousness were associated with significant changes on every measured breathing parameter, but the interactions of these effects with the deafferentations were small or nonsignificant. The vagus, however, appears to play its largest role during NREM. We hypothesize that while vagal afference functions during all states to terminate inspiration, during W and REM separate but functionally equivalent mechanisms of central origin supplement the vagus in facilitating the termination of inspiration. The absence of these mechanisms during NREM accounts for the increased vagal influence during this state.