Tourniquet hyperpnea and its modification by agents which alter cerebral blood flow

Mechanism of respiratory effects of methylxanthines

Neural respiratory responses to theophylline, aminophylline and ethylenediamine were determined in paralyzed, vagotomized and glomectomized cats whose end-tidal PCO2 and brain temperature were kept constant. Intravenous theophylline and aminophylline similarly stimulated respiration, but ethylenediamine had no effect. The following did not cause the response: muscular and mechanical factors, carotid body and vagal reflexes, spinally mediated mechanisms arising below C7, changes of arterial PCO2 or medullary ECF pH, changes of whole body metabolic rate or release of substances from the adrenal glands. Absence of suprapontine brain did not prevent the response. Pretreatment with a serotonin antagonist did not affect the response but two different dopamine antagonists caused its attenuation. When administered into the third ventricle, theophylline did not stimulate respiration, but both aminophylline and ethylenediamine, due to the latter's ability to mimic the inhibitory effects on neurons of gamma-aminobutyric acid (GABA), caused significant depression of respiration. We conclude that the neural respiratory response to systemically administered theophylline is mediated at the level of the brainstem, and somehow involves the action of the neurochemical dopamine. The failure of cerebroventricularly administered theophylline to stimulate respiration must be related to its inability to reach the appropriate neurons from the cerebrospinal fluid.

Evidence in man for a fast neural mechanism during the early phase of exercise hyperpnea

Recently, the rapid increase in ventilation at the onset of exercise has been attributed to reflexes stimulated by the concomitant increase in cardiac output. To evaluate these 'fast-humoral' hypotheses in supine man, the heart rate, ventilation, and end-tidal PCO2 and PO2 were observed during four procedures: the onset of mild dynamic exercise by the lower legs (1) with and (2) without inflation of occluding cuffs around the upper thighs, (3) rapid induction of circulatory occlusion at the level of the upper thighs, and (4) abrupt release of circulatory occlusion after 2.5 min of ischemia. Exercise resulted in abrupt hyperpnea, alveolar hyperventilation, and tachycardia whether or not there was circulatory occlusion. Circulatory occlusion engendered abrupt bradycardia and transient, hyperventilatory hyperpnea. Release of circulatory occlusion resulted in relatively large tachycardia and, after a delay, small hyperpnea and alveolar hypoventilation. The results demonstrate that the early response to exercise is not inherently isocapnic hyperpnea and that, contrary to the prediction of the fast-humoral hypotheses, the presumed increase in cardiac output following cuff release does not produce a ventilatory response similar to that of exercise. These findings support the existence of a neurally mediated factor during the early stages of exercise hyperpnea.

The definition of "Cheyne-Stokes rhythms"

The review of the literature on Cheyne-Stokes respiratory periods reveals enormous variation of the opinions expressed. The original description concerned periodicity characterized by rhythmic changes of respiratory phases and respiratory pauses in a relation of 60 : 15 seconds. In the respiratory phase there were 30 respirations of increasing depths and frequency at the beginning of the phase and decreasing depths and frequency at the end of the phase. Literature data about Cheyne-Stokes respiration comprise a multiplicity of all rhythymic forms. The duration of respiratory cycles varies between 12 and 130 seconds. The relation of the respiratory phase and respiratory pause between 6 : 4 or 75 : 70 seconds, and the number of breaths between 3 and 30 during one respiratory phase. Cheyne-Stokes periods were observed in health subjects as well as in patients with neurological, neurosurgical, cardiac, pulmonary and paediatric diseases. Cheyne-Stokes periods were explained as sequel of prolongation of circulation time between pulmonary alveoli and respiratory centre, through increased sensitivity of the respiratory centre to CO2, diminished sensitivity of the respiratory centre to CO2 and O2-deficit, local blood flow disturbances, section of pathways in the brain stem with disinhibition of basic rhythms, brain immaturity, alterations of consciousness, and respiratory obstructions. Rhythmic changes of the heart beat, of excitability of the heart muscle, of blood pressure, of EEG and of neurological and mental signs were observed. In spite of numerous observations detailed analysis of the respiratory cycle was performed in only a few cases. Major studies are lacking.

Left ventricular pressure responses in post-angiographic angina

Alterations in left ventricular end-diastolic pressure and in dp/dt observed in ten patients with coronary heart disease who developed angina pectoris following left ventricular cineangiography were compared with those of six other patients who developed angina spontaneously and with patients who underwent left ventricular cineangiography without experiencing angina. In the patients with post-angiographic angina there was a greater increase in end-diastolic pressure than that seen in the other patients, but there was no significant change in dp/dt. Changes in left ventricular pressure associated with post-angiographic angina would appear to reflect the combined effects of increased preload provided by the contrast material and of ventricular dysfunction including diminished compliance associated with angina. A rise in end-diastolic pressure greater than 20 mmHg following left ventricular cineangiography should alert the physician that the patient may be having myocardial ischemia.