Noninvasive respiratory support of juvenile rabbits by high-amplitude bubble continuous positive airway pressure.

Bubble continuous positive airway pressure (B-CPAP) applies small-amplitude, high-frequency oscillations in airway pressure (DeltaPaw) that may improve gas exchange in infants with respiratory disease. We developed a device, high-amplitude B-CPAP (HAB-CPAP), which provides greater DeltaPaw than B-CPAP provides. We studied the effects of different operational parameters on DeltaPaw and volumes of gas delivered to a mechanical infant lung model. In vivo studies tested the hypothesis that HAB-CPAP provides noninvasive respiratory support greater than that provided by B-CPAP. Lavaged juvenile rabbits were stabilized on ventilator nasal CPAP. The animals were then supported at the same mean airway pressure, bias flow, and fraction of inspired oxygen (FiO2) required for stabilization, whereas the bubbler angle was varied in a randomized crossover design at exit angles, relative to vertical, of 0 (HAB-CPAP0; equivalent to conventional B-CPAP), 90 (HAB-CPAP90), and 135 degrees (HAB-CPAP135). Arterial blood gases and pressure-rate product (PRP) were measured after 15 min at each bubbler angle. Pao2 levels were higher (p<0.007) with HAB-CPAP135 than with conventional B-CPAP. PaCO2 levels did not differ (p=0.073) among the three bubbler configurations. PRP with HAB-CPAP135 were half of the PRP with HAB-CPAP0 or HAB-CPAP90 (p=0.001). These results indicate that HAB-CPAP135 provides greater respiratory support than conventional B-CPAP does.

A new breath-holding test may noninvasively reveal early lung abnormalities caused by smoking and/or obesity.

BACKGROUND: Smoking and obesity are leading global causes of death. The aim of the present study was to develop a test to detect early lung abnormalities caused by smoking and/or obesity and to elucidate the underlying mechanisms and major contributory factors. METHODS: One hundred twenty-nine healthy adults, 20 to 40 years of age, with normal spirometry findings, were divided into the following five groups: 38 healthy subjects (15 female subjects); 46 smokers (5 female smokers); 18 overweight nonsmokers (2 female nonsmokers; normal body mass index [BMI], >or= 25 kg/m(2); range, 25.0 to 37.2 kg/m(2)); 19 overweight smokers (1 female smoker; BMI range, 25.2 to 33.5 kg/m(2)); and 8 ex-smokers (BMI range, 20.8 to 24.1 kg/m(2)). A modified pulse oximeter was employed for measuring the fall in pulse oximetric saturation caused by 20-s breath-holding (dSpo(2)) at resting end expiration in the sitting posture. RESULTS: In healthy subjects, dSpo(2) had no significant correlation with age (r(2) = 0.009; p = 0.66). In smokers, dSpo(2) correlated with both the number of pack-years (r(2) = 0.590; p < 0.001) and closing volume (CV)/vital capacity (VC) ratio (r(2) = 0.573; p < 0.001). In overweight nonsmokers, dSpo(2) increased significantly with BMI alone (r(2) = 0.667; p < 0.001). In overweight smokers, the largest increase in the mean dSpo(2) was observed. Multiple linear regression analysis suggested that BMI and CV/VC are the two major contributing factors determining dSpo(2) during breath-holding. In young former smokers, no significant increase in the mean dSpo(2) was observed (p = 0.77) a mean (+/- SD) duration of 5.2 +/- 2.9 years after the cessation of smoking. No significant difference in dSpo(2) was observed between men and women. CONCLUSIONS: A new test that measures oxygen saturation during breath-holding reveals early lung abnormalities in subjects who either smoke or are overweight, especially if these factors are combined. Peripheral airway abnormalities and/or lung volume reduction may play roles in the greater desaturation.

Ventilation and perfusion distribution during altered PEEP in the left lung in the left lateral decubitus posture with unchanged tidal volume in dogs.

Previous studies in anesthetized humans positioned in the left lateral decubitus (LLD) posture have shown that unilateral positive end-expiratory pressure (PEEP) to the dependent lung produce a more even ventilation distribution and improves gas exchange. Unilateral PEEP to the dependent lung may offer special advantages during LLD surgery by reducing the alveolar-to-arterial oxygen pressure difference {(A-a)PO2 or venous admixture} in patients with thoracic trauma or unilateral lung injury. We measured the effects of unilateral PEEP on regional distribution of blood flow (Q) and ventilation (V(A)) using fluorescent microspheres in pentobarbital anesthetized and air ventilation dogs in left lateral decubitus posture with synchronous lung inflation. Tidal volume to left and right lung is maintained constant to permit the effect on gas exchange to be examined. The addition of unilateral PEEP to the left lung increased its FRC with no change in left-right blood flow distribution or venous admixture. The overall lung V(A)/Q distribution remained relatively constant with increasing unilateral PEEP. Bilateral PEEP disproportionately increased FRC in the right lung but again produced no significant changes in venous admixture or V(A)/Q distribution. We conclude that the reduced dependent lung blood flow observed without PEEP occurs secondary to a reduction in lung volume. When tidal volume is maintained, unilateral PEEP increases dependent lung volume with little effect of perfusion distribution maintaining gas exchange.

Redistribution of blood flow and lung volume between lungs in lateral decubitus postures during unilateral atelectasis and PEEP.

The effect of left lung atelectasis on the regional distribution of blood flow (Q), ventilation (V(A)) and gas exchange on the right lung ventilated with 100% O2 was studied in anesthetized dogs in the lateral decubitus posture. Q and V(A) were measured in 1.7 ml lung volume pieces using injected and aerosolized fluorescent microspheres, respectively. Hypoxic pulmonary vasoconstriction (HPV) in the atelectatic lung shifted flow to the ventilated lung. The increased flow in the ventilated lung ensured adequate gas exchange, compensating for the hypoxemia due to shunt contributed by the atelectatic lung. Left lung atelectasis caused a compensatory increase in the ventilated lung FRC that was smaller in the right (RLD) than left (LLD) lateral posture, the effect of lung compression by the atelectatic lung and mediastinal contents in the RLD posture. The O2 deficit measured by (A-a)DO2 increased with left lung atelectasis and was exacerbated in the LLD posture by 10 cm H2O PEEP, a result of increased shunt caused by a shift in Q from the ventilated to the atelectatic lung. The PEEP-induced O2 deficit was eliminated with inversion to the RLD posture.

Spatial distribution of ventilation and perfusion in anesthetized dogs in lateral postures.

We aimed to assess the influence of lateral decubitus postures and positive end-expiratory pressure (PEEP) on the regional distribution of ventilation and perfusion. We measured regional ventilation (VA) and regional blood flow (Q) in six anesthetized, mechanically ventilated dogs in the left (LLD) and right lateral decubitus (RLD) postures with and without 10 cmH(2)O PEEP. Q was measured by use of intravenously injected 15-microm fluorescent microspheres, and VA was measured by aerosolized 1-microm fluorescent microspheres. Fluorescence was analyzed in lung pieces approximately 1.7 cm(3) in volume. Multiple linear regression analysis was used to evaluate three-dimensional spatial gradients of Q, VA, the ratio VA/Q, and regional PO(2) (Pr(O(2))) in both lungs. In the LLD posture, a gravity-dependent vertical gradient in Q was observed in both lungs in conjunction with a reduced blood flow and Pr(O(2)) to the dependent left lung. Change from the LLD to the RLD or 10 cmH(2)O PEEP increased local VA/Q and Pr(O(2)) in the left lung and minimized any role of hypoxia. The greatest reduction in individual lung volume occurred to the left lung in the LLD posture. We conclude that lung distortion caused by the weight of the heart and abdomen is greater in the LLD posture and influences both Q and VA, and ultimately gas exchange. In this respect, the smaller left lung was the most susceptible to impaired gas exchange in the LLD posture.