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Biomedical subjects

D R Hazlett

Publications and source records attributed to D R Hazlett.

13 recordsLinked to original sources
PubMed1977

Temporal effects in the estimation of pulmonary diffusing capacity.

Steady state estimates of the pulmonary diffusing capacity for carbon monoxide (DLCO) require measurement of the uptake and the average alveolar partial pressure of carbon monoxide (PACO). The expired alveolar sample obtained by different experimental methods and/or breathing patterns rarely represents the actual PACO. It is widely accepted that nonuniform distribution of ventilation, diffusion and perfusion causes discrepancies in the measurement of diffusing capacity. tan additional source of error in choosing PACO arises in the sampling time chosen by the experimental method. A theoretical study of a ramp-with-pause and a square breathing pattern demonstrates that the sample-time error exists even in the homogeneous lung. The study shows for the homogeneous lung that the correct fractional concentration of alveolar carbon monoxide (FAV) occurs at a time (TAV), one-half of a breathing period after the effective inspiration time (TI) for the two very different breathing patterns. TI is well-defined in relation to any breathing pattern which can be approximated by ramps and pauses. If TAV and the sample time chosen by the experimental method are known, then the measured DLCO can be corrected to the actual diffusing capacity (DL). The theory agrees with experimental results and computer simulations of inhomogeneous lungs from the literature. This agreement suggests that the theory for the homogeneous lung is also relevant to the inhomogeneous lung.

Carbon Monoxide↗
PubMed1977

Systemic vascular performance in endotoxic shock.

Sixteen dogs were studied in an effort to investigate certain peripheral vascular and metabolic parameters in endotoxic shock. Cardiopulmonary bypass was instituted for 12 of the dogs to study systemic parameters at constant circulatory flow rates. From these studies, it appears that endotoxin is capable of initiating profound hemodynamic and metabolic changes. Initially, cardiac output and arterial pressure drop precipitiously, despite a transient rise in systemic and pulmonary vascular resistance. Subsequently, peripheral arterial pressures and systemic vascular resistance continue to decline, even if arterial flow remains at constant levels. Oxygen extraction by peripheral tissues decreases after endotoxin injection, despite adequate oxygen availability and constant hemoglobin levels.

Animals↗
PubMed1976

Time delay effects in the estimation of pulmonary diffusing capacity.

Steady state estimates of the pulmonary diffusing capacity for carbon monoxide require measurement of the uptake and the average partial pressure of CO in the lung. The expired alveolar sample obtained by different experimental methods and/or breathing patterns rarely represents the actural average alveolar partial pressure. This error in choosing the correct alveolar sample arises in the sampling time chosen by the experimental method. The time (TAV) at which the correct alveolar sample (FAV) is obtained occurs one-half of a breathing period after the effective inspiration time. If TAV and the sample time chosen by the experimental method are known then the measured diffusing capacity can be corrected to the actual diffusing capacity.

Carbon Monoxide↗