Maturation of hypoxic ventilatory response of the newborn lamb.

The ventilatory response to acute hypoxia was studied in unanesthetized newborn lambs before and after carotid body denervation. Animals studied immediately following operative delivery were compared with a second group who were studied in the 2nd wk of postnatal life. Response time was defined as the interval between the decrease in oxygen saturation in the aortic arch and an increase in tidal volume or ventilatory rate. Animals in the older group demonstrated a significantly shorter response time than those studied immediately following delivery (1.8 s vs. 5.7 s). A ventilatory response was also elicited in carotid body-denervated animals in both study groups. Mean response time following denervation was 29.5 s for the younger and 12.5 s for the older animals. The data suggest that the development of a rapid, carotid body-mediated hypoxic ventilatory response occurs gradually during the first days of postnatal life, and that the central hypoxic response of the fetus (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42:630-635, 1977) persists into postnatal life.

Is continuous transpulmonary pressure better than conventional respiratory management of hyaline membrane disease? A controlled study.

The influence of continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) on mortality and complication rates in severe hyaline membrane disease (HMD) was evaluated in a randomized, prospective study. Patients were admitted to the study if the Po2 was less than 50 mm Hg with FiO2 greater than 0.6. Twenty-four patients in each of three weight groups were equally divided between treatment and control groups. The treatment regimen included CPAP (6 to 14 cm H2O) for spontaneously breathing patients and PEEP for patients requiring mechanical ventilation for apnea or hypercapnia (Pco2 greater than 65 mm Hg). Control patients received oxygen and were mechanically ventilated if they had apnea, hypercapnia, or Po2 less than 50 mm Hg with FiO2 greater than 0.8. Oxygenation improved after the start of CPAP or PEEP; however, Pco2 rose after CPAP was initiated. There was no significant difference between treatment and control groups in mortality, requirement for mechanical ventilation, or incidence of pulmonary sequelae. The incidence of pulmonary air-leak was increased with Peep. the findings suggest that CPAP and PEEP have not significantly altered the outcome of HMD.

Application of the hot-wire anemometer to respiratory measurements in small animal.

A hot-wire anemometer was evaluated to determine its suitability for measurement of small tidal volumes. Used with a constant background flow of gas, the output of the hot-wire anemometer was linear and independent of respiratory frequency, temperature, and humidity. The change in output with CO2 concentration was negligible within the physiologic range. The use of a background flow eliminates the need for one-way valves, minimizes dead space, and maintains the flow velocity past the hot wire within its range of linear response.