Byungchul Ahn

Heart rate response to breath-holding during supramaximal exercise

SummaryThe cardiovascular responses to breath-holding (BH) during short-lasting supramaximal exercise (415 W) on a cycle ergometer were investigated in 15 healthy male subjects. The arterial oxygen saturation, heart rate (HR), endtidal PO2 and PCO2 were continuously monitored. Firstly, 15 subjects performed exercise during BH, preceded by air breathing (air-BH test), and secondly, exercise without BH. Then 9 of the subjects performed the same procedure as in the air-BH test, except that all subjects breathed 100% O2 for 1 min before apnoea (O2-BH test). In 2 of these subjects, the systemic arterial blood pressure was continuously measured via a catheter in the radial artery and plasma catecholamine concentration [CA] was also measured both during the air-BH and the O2-BH tests. In the later period of the air-BH test, the high HR level became progressively depressed. This response, however, was absent in the O2-BH test. There was a late increase in the arterial blood pressure in both tests, and both tests produced hypercapnia. Only the air-BH test resulted in hypoxia, substantial hypertension and HR-depression. The increase in plasma CA was similar in both tests. The marked HR-depression demonstrated here is ascribed mainly to activation of the peripheral arterial chemoreceptors by asphyxia, and partially to baroreceptor activity due to elevated blood pressure.

Effect of Unilateral Pulmonary Vagotomy on Respiratory Control in Man

We studied the breathing pattern and pulmonary function at rest, and ventilatory responses to progressive hypoxia and hypercapnia in 7 awake patients who had undergone esophageal-carcinoma resection with sectioning of the right pulmonary vagal branch by lymphadenectomy. Twelve control patients, who had received the same surgery without vagotomy, were also studied by the same protocol. Two months after the operation, both patient groups demonstrated substantial depressions in FVC and FEV1.0, and slight augmentations in breathing frequency, minute ventilation, and occlusion pressure at 0.2s (P0.2) at rest. In the vagotomized group, the occlusion pressure responses to hypercapnia (delta P0.2/delta PaCO2) and hypoxia (delta P0.2/delta SaO2) in terms of response curve slope increased from 1.3 +/- 1.2 to 1.9 +/- 1.1 cm H2O/Torr and from 0.29 +/- 0.19 to 0.88 +/- 0.53 cm H2O/% (p less than 0.05), respectively. Contrary to the vagotomized patients, the nonvagotomized control group exhibited no significant changes in ventilatory chemosensitivities. Furthermore, when comparing the control and vagotomized groups, postoperative ventilatory chemosensitivity responses in terms of both hypercapnic and hypoxic occlusion pressure responses were significantly higher in the latter. We suggest that (1) due to the development of the substantial mechanical limitation in pulmonary functions, the Hering-Breuer inflation reflex became activated after surgery, and (2) a diminished Hering-Breuer reflex effect to inhibit the respiratory centers by unilateral vagotomy may have resulted in augmented ventilatory chemosensitivities.

Importance of Arterial Chemoreceptors for Cardiorespiratory Responses to Static Exercise in Man

Static isometric exercise leads to a rapid heart rate acceleration and pulmonary hyperventilation (Miyamoto et al., 1987). The heart rate acceleration is known as a muscle-heart reflex, originates in muscle receptors affected by noxious chemical and mechanical stimulation, and is mediated by group III and IV afferents (Gelsema et al., 1983). The mechanism of the hyperpnea is uncertain, as is also the role of chemical drive in both cardiac and respiratory events of static exercise.

Possible Involvement of Peripheral Chemoreceptor Mechanism in Bradycardia Observed During Breath Holding with Supramaximal Exercise

It is often seen that the breath is held during strenous exercise such as 100m or 200m dash. The characteristic features in this maneuver are that exercise intensity is very vigorous and duration is very short. To our knowledge, no detailed observation has been conducted on the cardiopulmonary responses during this particular physical performance.

CO2 Chemoreflex in Spinal Man

In this study we tested the hypothesis that the stimulatory hypercapnic ventilatory response (HCVR) would be less in quadriplegic patients. Apart from the sheer exclusion of a substantial part of the effector of the respiratory control system due to paralysis of the respiratory muscles of the chest and abdominal wall, two lines of evidence suggest such a possibility. First, these muscles contain a rich network of mechanoreceptors, muscle spindles, and tendon organs, which are classified as proprioceptors. There is evidence showing that afferent information from these proprioceptors exerts, via ascending spinal pathways, a reflex effect on the central control of respiration, modulating the descending drive to phrenic and intercostal spinal motoneurons (Shannon, 1986). Second, chemoreceptor afferents might have a facilitatory effect on the descending drive to respiratory muscle neurons independent of the proprioceptive influences. Recent studies have shown that hypercapnia increases both internal intercostal (Fregosi and Bartlett, 1989) and abdominal expiratory (Ledlie et al.,1983) nerve activities in the absence of proprioceptive feedback from the body wall.