Invasive Cardiopulmonary Exercise Testing (iCPET) on Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME / CFS) patients shows a characteristic pattern of “preload failure” (PLF) that could be associated with postural orthostatic tachycardia syndrome (POTS) and/or post-exertion malaise (PEM).
The PLF comes in 2 forms, a high flow and a low flow. The low flow form may be caused by a failure to reduce venous compliance with exercise or a pre-existing reduced overall blood volume. However, the latter is less likely because the PLF persists even when one liter of saline is given to increase the blood volume just prior to the iCPET study. On the other hand, the high flow PLF may be caused by peripheral arterial-venous shunt effects or deficient oxygen delivery or utilization. A final explanation is that blood travels through the peripheral capillary system normally but cellular oxygen uptake and/or utilization by the mitochondria is deficient.
ME / CFS patients impaired with PLF, as diagnosed by a single iCPET or by sequential iCPET, will be further evaluated. This evaluation will measure large vessel vascular capacitance and blood volume, additional diagnostic testing (i.e., screening for adrenal insufficiency, tilt-table testing, nerve conduction studies) and the presence of peripheral shunting and oxygen delivery. Therapeutic intervention (i.e., hydration, increased sodium intake, β-adrenergic receptor antagonists, fludrocortisone, pyridostigmine, and/or midodrine), compression stockings, and monitored exercise training will also be employed based upon individual patient findings.