We examined the prevalence of dirofilariasis (DF) and its effects on VA/Q distribution in mongrel dogs. Dirofilaria was tested with routine techniques (direct smear and microfilaria concentration technique) and autopsy in 36 dogs. Continuous distributions of VA/Q ratios by multiple inert gas method were determined in 6 dogs with DF (DF group) and 9 dogs without DF (non-DF group).
1) The prevalence of DF was 16.7% (6/36). Autopsy was more accurate than the routine techniques for detection of DF. The routine techniques revealed one false negative case (1/6), but they seemed to be useful to detect DF reliably.
2) PaO2 was significantly lower in the DF group than in the non-DF group (72.4±10.1 and 98.1±9.8 torr, respectively, p<0.001). LogSD(Q) tended to be larger in the DF group then in the non-DF group (1.01±0.37 and 0.64±0.12, respectively, p<0.1).
3) PaO2 correlated inversely with LogSD(Q) (r=-0.60, p<0.025) and shunt blood flow, i.e. VA/Q=0 (r=-0.54, p<0.05). In 3 of the DF group, more than 10% of blood flow distributed to units of low VA/Q ratios less than 0.01.
In conclusion, mongrel dogs with DF are substantially inappropriate for physiological studies on the cardiopulmonary system.
