Repeated administration of frusemide does not offer an advantage over single dosing in attenuating exercise‐induced pulmonary hypertension in Thoroughbred horses

Abstract

Summary The objective of the present study was to ascertain whether administration of a second dose of frusemide would attenuate exercise‐induced pulmonary hypertension more than a single dose. Right atrial, right ventricular and pulmonary vascular pressures were determined in 7 healthy, sound, exercise‐trained Thoroughbred horses at rest and during exercise (14.2 m/s + a 3.5% uphill grade) performed at maximal heart rate (217 ± 3 beats/min [mean ± s.e.]). Horses were studied during the following 3 treatments in random order 7 days apart: control (no medication), frusemide single dose (250 mg i.v. 4 h pre‐exercise), and frusemide double dose (250 mg i.v., 4 h pre‐exercise + 250 mg i.v. 2 h pre‐exercise). In the control study, exercise resulted in significant (P<.05) right atrial as well as pulmonary arterial, capillary and venous hypertension. In the frusemide single dose experiments, a significant (P<.05) attenuation of the exercise‐induced rise in right atrial and pulmonary vascular pressures was observed. However, compared with frusemide single dose experiments, significant changes in the exercise‐induced right atrial and pulmonary arterial, capillary and venous hypertension were not observed in the frusemide double dose experiments. Therefore, it is concluded that administration of an additional dose of frusemide is unlikely to affect the severity of EIPH in racing Thoroughbred horses more than a single dose.

Effect of instillation into lung of autologous blood on pulmonary function and tracheobronchial wash cytology

“…The theory of the alveolo-arterial membrane rupture induced by an excessive transmural pressure (West et al 1993) is generally accepted by the scientific community (Slocombe 2001). This hypothesis seems to be confirmed by recent works showing that the use of nasal strip and/or frusemide may decrease the incidence of EIPH (Goetz et al 1999;Geor et al 2001;Kindig et al 2001) while inspiratory obstruction increases the transmural capillary pressure gradient (Ducharme et al 1999).…”

Pulmonary Hemodynamics

“…It has been observed that the blood flow in these capillaries occurs despite alveolar pressures being, at times, in excess of the capillary blood pressure (Lloyd and Wright, 1960;Thomas et al, 1961). Additional support for this suggestion derives from studies implying that capillary resistance increases when one removes the influence of the alveolar surface tension (Goetz et al, 1999;Hedenstierna et al, 1984), thus suggesting that the alveolar surface tension promotes capillary blood flow. Studies in which vascular resistance measurements were coupled with direct visualization of this microvasculature indicate that the pulmonary arterial and the venous vascular resistance increase with an increase in alveolar surface tension (by reducing surfactant), while the capillary resistance decreases with a subsequent increase in the capillary distension and recruitment (Nieman et al, 1988).…”

“…In fact, several investigators have observed open vessels in alveolar corners under zone I conditions (Goetz et al, 1999;West and Dollery, 1960) and have found that up to 15% of cardiac output goes through lungs in zone I (Koyama et al, 1989). This perfusion persists despite the fact that the vessels in the adjacent alveoli are collapsed as a result of the relatively high alveolar pressures (Anthonisen and Milic-Emili, 1966;Keilholz et al, 2001;Brudin et al, 1994;Kosuda et al, 2000).…”

“…This is a much lower driving pressure for the blood flow than the systemic circulation, where the arterial-venous pressure gradient is approximately 90 mmHg in humans. Table 1 summarizes the pulmonary hemodynamic parameters for other species from different studies (Barer and Nusser, 1957a;Drougas et al, 1996;Holm et al, 1998;Morris et al, 2000;Grant and Canty, 1989;Baxter et al, 1952;Duke and Stedeford, 1960;Chen et al, 2005;Yuan et al, 2011;Liu et al, 2005;Emery et al, 2001;Fesler et al, 2006;Chick et al, 1988;Franceschi et al, 2013;Chaliki et al, 2002;Romand et al, 1994;Takeda et al, 1987;Johnson et al, 1992;Ravikumar et al, 2011;Reddy et al, 1995;Polglase et al, 2006;Newman et al, 1993;Nachar et al, 2001;Krebs et al, 2007;Hinder et al, 1998;Pennington et al, 1992;Patschova et al, 2010;Stickland et al, 2007;Li et al, 2013;Goetz et al, 1999;Tournoux et al, 2011;Ortiz et al, 2002;Ullrich et al, 1999). Although the blood flow through the pulmonary circulation is essentially the same as the blood flow through the systemic circulation, the pulmonary vascular resistance is 10-to 15-fold lower than the systemic vascular resistance.…”

Exercise-induced pulmonary haemorrhage in horses – review

“…It has been shown that the administration of furosemide 4 h before each competition reduces the risk of EIPH (Pascoe 1997;Soma et al 2000). In addition, Goetz et al (1999) showed that an additional dose of furosemide before the competition does not achieve a greater attenuation of pulmonary vascular pressure. The same authors concluded that this additional dose does not diminish the severity of the EIPH, compared to the use of a single dose.…”