Does menstrual cycle phase affect lung diffusion capacity during exercise?

Resting lung diffusing capacity (DLCO) decreases during the early and late-follicular phases of the menstrual cycle presumably due to capillary blood volume (VC) changes; however, it is not known if these differences exist during exercise. We hypothesized that DLCO would increase during the mid-luteal phase of the menstrual cycle due to increases in VC. Eight normally menstruating females (21.4 ± 0.7 yrs) were studied. Subjects completed a discontinuous treadmill V˙O2max test during the early-follicular (EF), late-follicular (LF), and mid-luteal (ML) phases of the menstrual cycle. Metabolic measurements were made from a breath-by-breath automated cart, and DLCO via the single-breath exhalation technique during exercise. During exercise, DLCO was lesser during EF compared to ML at 90% and 100%V˙O2max (p < 0.05) (90%: 37.8 ± 3.7 EF vs 41.6 ± 4.0 ML, 100%: 37.7 ± 3.7 EF vs 42.6 ± 4.3 ML mL/mmHg/min). VC was significantly greater during the ML phase when compared to the EF at 80%, 90%, and 100%V˙O2max. These results demonstrate DLCO and VC are influenced by the menstrual cycle during heavy exercise.