Premium
Pulmonary capillary pressure in horses undergoing alteration of pleural pressure by imposition of various upper airway resistive loads
Author(s) -
DUCHARME N. G.,
HACKETT R. P.,
GLEED R. D.,
AINSWORTH D. M.,
ERB H. N.,
MITCHELL L. M.,
SODERHOLM L. V.
Publication year - 1999
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.1999.tb05183.x
Subject(s) - medicine , pulmonary wedge pressure , cardiology , pulmonary artery , anesthesia , blood pressure
Summary We hypothesised that changes in pleural pressure induced by resistive breathing would affect transmural pulmonary artery, pulmonary capillary, and pulmonary wedge pressures. Seven horses were assigned to exercise with each of 4 upper respiratory resistive loads in random order at intervals of at least 2 days: 1) control — no added resistive loads; 2) inspiratory resistive load (I obst ) — left laryngeal hemiplegia; 3) expiratory resistive load (E obst ) — one‐way valve in the right nostril; and 4) combined inspiratory and expiratory resistive loads (CIE obst ) — left nostril occlusion. On each occasion, the horses performed an incremental exercise protocol consisting of exercise episodes of 3 min duration at 75, 90, and 100% of maximal heart rate (HR max ). Pulmonary artery and oesophageal pressures were recorded continuously. Subsequent analysis was carried out on the pulmonary arterial pressure signal with the oesophageal pressure signal subtracted, hence the pulmonary vascular pressures in this paper approximate transmural pressures. Pulmonary vascular pressures, heart rate, and arterial blood gas tensions were measured at each level of exercise. Pulmonary capillary and pulmonary wedge pressures were determined from the pulmonary artery waveform after dynamic occlusion of a branch of the pulmonary artery. During exercise, peak expiratory oesophageal pressure was more positive in horses with E obst and CIE obst (adjusted means=43, and 39 mmHg, respectively) compared with control (adjusted mean=23 mmHg) (P = 0.0001). Peak inspiratory oesophageal pressure was more negative in horses at exercise with I obst and CIE obst (adjusted means=‐42 and ‐39 mmHg, respectively) compared with control (adjusted mean=‐26 mmHg)(P = 0.0012). E obst was associated with an increase in mean oesophageal pressure while I obst was associated with a decrease in mean oesophageal pressure. There were significant increases in mean pulmonary artery pressure in horses with CIE obst (adjusted means = 82 mmHg) and in pulmonary wedge pressure in horses with CIE obst and I obst (adjusted means=51, and 55 mmHg, respectively) when compared to control (73 and 42 mmHg, respectively) (P = 0.0001). Pulmonary capillary pressure was significantly increased in horses with CIE obst or I obst (adjusted means=61 mmHg, 63 mmHg, respectively) when compared to control (adjusted mean=50 mmHg)(P = 0.0001). At maximal exercise intensity with inspiratory obstruction, the mean oesophageal (pleural) pressure was ‐17 mmHg while the mean pulmonary capillary pressure was 77 mmHg. The latter exceeds the reported 75 mmHg threshold for capillary failure in horses. We conclude that inspiratory resistive breathing can lead to a significant increase in transmural pulmonary capillary pressure which may contribute to loss of capillary integrity and rupture.