In six open-chest dogs, electrocardiogram- (ECG) controlled pulmonary arterial occlusion was performed during the control period and during the infusions of serotonin and histamine. A temporal series of instantaneous pulmonary capillary pressure and the longitudinal distributions of vascular resistance and compliance were evaluated in the intact left lower lung lobe. In the control period, we found a significant phasic variation of pulmonary capillary pressure (Pc) with the cardiac cycle. The ratio of arterial to venous resistances (Ra/Rv) was 6:4, and the ratio of arterial to capillary compliances (Ca/Cc) was 1:11. During the infusions of serotonin and histamine, Pc showed similar phasic variations, despite significant hemodynamic changes induced by these agents. Serotonin predominantly increased Ra, whereas histamine predominantly increased Rv. The ratio of Rv to the total resistance decreased significantly from 0.42 to 0.32 during the infusion of serotonin and increased significantly to 0.62 during the infusion of histamine. The data suggest that phasic Pc determined by ECG-controlled arterial occlusion reflects the pulsatility in the pulmonary microvascular bed under control conditions and after alterations of the pulmonary vascular resistance by serotonin and histamine.
We conducted a laboratory study on six commercially available heat and moisture exchangers in order to determine and compare their water retaining efficiency and their contribution to airway resistance. The Gambro-Engström Edith Flex device was the most desirable of the six devices we evaluated in terms of its water retaining efficiency. The NMI Pneumoist 1 and the Siemens Servo Humidifier 153 units had good water retaining capacity but their higher airflow resistance need close monitoring, especially after prolonged clinical use. The Pall HME 15-22 and the Portex Humid-Vent 1 devices were also efficient in water retaining capacity. The Pall also demonstrated low airflow resistance and the minimum increase in airflow resistance after water immersion. The pathogen filtering capacity of the Pall should also be considered an additional advantage, especially in infected patients. The Terumo Breathaid device performed worst of all six devices, but it was still better than no HME at all.
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