Heart rate variability in horses with and without severe equine asthma.

Abstract

BACKGROUND: Equine asthma in severe form (severe equine asthma [sEA]) shares remarkable similarities with human asthma. Human studies detected changes in the autonomic nervous system function in asthmatic patients based on heart rate variability (HRV) analysis. STUDY DESIGN: Observational study. OBJECTIVES: To investigate the relationship between sEA and HRV in horses. METHODS: Twenty horses diagnosed with sEA and 20 asymptomatic (non-sEA) horses were investigated. SEA horses showed clinical signs. The RR intervals of the ECG were recorded for 1&#x2009;h at rest between 9&#x2009;AM and 11&#x2009;AM using a heart rate (HR) monitor. HRV data were calculated using Kubios software. Parameters recorded for the sEA and non-sEA groups were compared using one-way MANOVA model. The significance level was set at &#x3b1;&#x2009;=&#x2009;0.05. RESULTS: SD2 (mean 99.6&#x2009;&#xb1;&#x2009;SD 25.3 vs. 42.5&#x2009;&#xb1;&#x2009;17.1), SDNN (82.7&#x2009;&#xb1;&#x2009;20.7 vs. 41.3&#x2009;&#xb1;&#x2009;14.3), TINN (398.1&#x2009;&#xb1;&#x2009;104.9 vs. 209.3&#x2009;&#xb1;&#x2009;71.9), SD2/SD1 ratio (1.7&#x2009;&#xb1;&#x2009;0.2 vs. 1.1&#x2009;&#xb1;&#x2009;0.3), Total power (4740.2&#x2009;&#xb1;&#x2009;1977.9 vs. 1503.0&#x2009;&#xb1;&#x2009;1179.3), LF (2415.3&#x2009;&#xb1;&#x2009;1072.4 vs. 707.4&#x2009;&#xb1;&#x2009;649.9), SD1 (60.9&#x2009;&#xb1;&#x2009;15.9 vs. 39.2&#x2009;&#xb1;&#x2009;14.1), RMSSD (86.0&#x2009;&#xb1;&#x2009;22.6 vs. 55.3&#x2009;&#xb1;&#x2009;19.8) and HF (1575.8&#x2009;&#xb1;&#x2009;902.5 vs. 578.1&#x2009;&#xb1;&#x2009;491.1) were lower in sEA horses compared with the non-sEA horses (p&#x2009;<&#x2009;0.01 for each variable). SD2, SDNN, TNN, the SD2/SD1 ratio and Total power showed the greatest discriminatory power in differentiating the sEA and non-sEA groups. MAIN LIMITATIONS: Small sample size. CONCLUSION: Our findings indicate that like humans, asthmatic horses show an overall reduction in autonomic control. A relative increase of the parasympathetic modulation of the heart was also observed. After further investigations, HRV measurement might be a non-invasive approach to monitor autonomic nervous system responses of sEA horses.