Heart and lung adaptations to pregnancy and lactation in a crocidurine shrew

Heart and lung mass, rate of oxygen consumption (V̇_O2 ), respiration rate (fr), tidal volume (Vt), and heart rate (fh), were measured at rest and thermoneutrality in the shrew Crocidura russula monacha [(This shrew is claimed to be Crocidura suaveolens (Catzeflis, F., T. Maddalena, S. Hellwing and P. Vogel (1985). Unexpected findings on the taxonomic status of East Mediterranean Crocidura russula auct. (Mammalia, Insectivora). Zeitschrift fur Säugetierkunde 50: 185-201)] in nullipar (N), pregnant (P) and lactating (L) females. The heart mass of N females is large (0.86% of body mass) but fh is slow (70% of that expected by mammalian allometry), while lung mass is small (87% of expected) and fr is high (47% above expected). The 31% higher than expected expired ventilation (V̇e) matches the 25% higher than expected V̇_O2 . In P females the fh of 560 min^-1 did not change but it increased in L females to 620 min^-1. V̇e did not change in P females but decreased in L females from 11.3 ml · min^-1 to 10.1 ml min^-1. The normal Vt decreased in P and L females from 47.3 μl to 38.4 μl and 37.8 μl respectively. The lower than expected resting fh of N females may provide sufficient scope for increased heart work and oxygen supply during exercise. The large heart may be more efficient. Hyperventilation in N females is indicated by the calculated relatively high fractional concentration of oxygen in expired air (Fe_O2 ), and low fractional concentration of CO₂ in expired air (Fe_CO2 ) (17.7% and 3.2% respectively), the high oxygen partial pressure in alveolar gas (Pa_O2 ) and low alveolar CO₂ (Pa_CO2 ), 119 and 34 Torr respectively, which facilitate O₂ transport through the lung air-blood barrier. The elevated V̇O₂ in P and L females is achieved by increased respiratory efficiency from the normal 15%, to 24% and 29% respectively.