Respiration physiology
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The expiratory minute volume (Ve), respiratory frequency (f), tidal volume (VT), carbon dioxide production (Vco2), and end-tidal carbon dioxide concentration (FETCO2) and pressure (PETCO2) were measured at monthly intervals in 12 normal women during pregnancy and two, six and 12 weeks, and six months postpartum. At eacy study, measurements were made sitting at rest and during steady-state exercise at 306 kpm/min on a bicycle ergometer. During pregnancy, a significant increase in VE occurred, both at rest and during exercise, due to a significantly greater VT. ⋯ However, resting physiologic dead space increased during pregnancy. Alveolar ventilation (VA) was calculated on the basis of three alternative assumptions: (1) that PETCO2 during exercise accurately reflects mean alveolar PCO2; (2) that the physiological dead space does not change during exercise; and (3) that mean alveolar PCO2 does not change from rest to exercise. Exercise VA, calculated on the basis of any of these three assumptions, is greater during pregnancy than postpartum.
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Using previously inserted catheters, 11 dogs native to high altitude (7.5-23 kg bwt) were studied standing and unsedated in Cerro de Pasco, Peru at 4350 meters. Hemoglobin (Hb), hematocrit (Hct), O2 and CO2 contents, PO2, PCO2 and pH were measured in simultaneously obtained arterial and mixed venous blood samples. Blood pressures were measured in the pulmonary artery and the left ventricle and cardiac output (Q) was determined by dye dilution. ⋯ Marked hyperventilation was observed (PACO2, 25.6 mm Hg) however, pH was normal. Cardiac output was normal (average 162 plus or minus 39 ml/min/kg). Moderate pulmonary arterial hypertension was observed in the presence of normal left ventricular end diastolic pressure suggesting increased pulmonary vascular resistance.
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Respiration physiology · Mar 1975
Occlusion pressure as a measure of respiratory center output in conscious man.
The output of the "respiratory centers" has been estimated by measuring ventilation, inspiratory muscle power, EMG of the diaphragm, and by various other means, each of which has serious disadvantages. The static pressure generated by the inspiratory muscles at FRC against an obstructed airway is here suggested as a useful alternative. Ten conscious, normal, sitting human subjects were subjected to CO2 rebreathing (Read, 1967) and their airways were occluded at end-expiration at intervals without the subjects being aware in advance. ⋯ The P0.1 is independent of pulmonary mechanics. Since it measures the rate of rise of inspiratory activity and not the peak activity it is also independent of mechanisms that alter the respiratory pattern by affecting inspiratory duration, in particular the vagal volume-related inspiratory-inhibitory reflex. It is concluded that measurements of P0.1 represent a useful index of the output of the respiratory centers.