TIDAL VOLUME, OXYGEN UPTAKE, CARDIAC OUTPUT, AND BODY SURFACE IN THE CAT

Twenty-two cats were studied under chloralose anesthesia. When animals breathed pure oxygen in a closed circuit especially set for spirogram recording, respiratory rate, tidal volume, minute volume, and oxygen uptake of 19 cats averaged 15 breaths/min, 26 ml, 0.380 liter/min, and 18.5 ml/min, respectively. Cardiac output of 11 cats, determined by simultaneous measurements after Fick and Stewart-Hamilton methods, averaged 234 and 184 ml/min, respectively. Statistical analysis shows a high degree of individual variability partially dependent on body size. Body surface was directly measured in 12 animals and a coefficient for prediction of body surface on a body weight basis was calculated: m2 = 0.087 kg2/3. When corrected per unit of body surface, the range of individual oxygen uptake in 19 cats was reduced and it averaged 113/ml min m2. Similar correction of cardiac output was not equally effective.

ROLE OF CEREBRAL FLUIDS IN CONTROL OF RESPIRATION AS STUDIED IN UNANESTHETIZED GOATS

Respiratory responses to inhaled CO2 were measured in unanesthetized goats during repeated perfusions of the ventriculocisternal system through chronically implanted cannulas. [HCO3–] and pH were measured in carotid loop blood and cisternal outflow. Average steady-state alveolar ventilation increased fourfold when cerebrospinal fluid (CSF)-[HCO3–] was reduced from 30 to 15 mm/liter at constant, normal CO2 pressure or threefold when CSF pH changed from 7.32 to 7.21 at constant, normal CSF-[HCO3–]. Sensitivity was two- to sevenfold greater than reported for anesthetized animals. At constant CSF pH the ventilatory response to inhaled CO2 was 60% of the isobicarbonate response. Pco2 in cisternal outflow was shown to approximate that in cerebral tissue. HCO3– flux was measured as a function of CSF-[HCO3–] and concentration profiles between CSF and capillary blood were considered. Alveolar ventilation is a single linear function of [H+] in tissue fluid located two-thirds to three-fourths of the distance along the functional concentration gradient of HCO3– between CSF and blood at all values of Pco2 and CSF-[HCO3–] which we investigated.

MEASUREMENT OF UPPER AND LOWER AIRWAY RESISTANCE AND CONDUCTANCE IN MAN

The resistances to flow in the upper (Ruaw) and lower (Rlaw) airway of human lungs were measured simultaneously with total airway resistance (Raw) and the volume of thoracic gas (Vtg) using the plethysmographic method and lateral pressure taps at the tracheal and oral levels. Ruaw is found to decrease slightly in a curvilinear fashion with increasing Vtg while its reciprocal, Guaw, is linearly related to Vtg with a negative Vtg intercept in normal subjects. Lower airway conductance (Glaw) is linearly related to Vtg with a slope of approximately 1.0 liters/sec per cm H2O per liter. From the partitioned resistances it is deduced that total airway conductance (Gaw) is curvilinear but approximately linear over the majority of the Vtg. A method of calculating resistance and conductance in the upper and lower airways from Raw versus Vtg data is presented using the equation Raw = Vtg/(A @#X002B; B Vtg) where B2/A @#X003D; dGlaw/ dVtg. Three hundred and sixty-two records of Raw versus Vtg data from 22 normal, asthmatic, and bronchitic subjects are then evaluated by this method and the results compared to those obtained by direct measurement.

intrathoracic or lower airway conductance; intrathoracic or lower airway resistance; extrathoracic or upper airway conductance; extrathoracic or upper airway resistance

Submitted on November 8, 1963