Hypocapnia is a biological marker for orthostatic intolerance in some patients with Chronic Fatigue Syndrome

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[Note: Hypocapnia is a state of reduced carbon dioxide in the blood resulting from deep or rapid breathing or ‘hyperventilation.’ Orthostatic intolerance is the development of symptoms when standing upright that are alleviated when reclining.]

Journal: Dynamic Medicine. 2007 Jan 30;6(1):2 [E-publication ahead of print]. This is an Open Access article. You may access the full text of the article free of charge at http://www.dynamic-med.com/content/pdf/1476-5918-6-2.pdf

Authors: Natelson BH, Intriligator R, Cherniack NS, Chandler HK, Stewart JM.

PMID: 17263876

Context: Patients with Chronic Fatigue Syndrome and those with orthostatic intolerance share many symptoms, yet questions exist as to whether CFS patients have physiological evidence of orthostatic intolerance. [Symptoms when standing upright that are alleviated when reclining.]

Objective: To determine if some CFS patients have increased rates of orthostatic hypotension [low blood pressure], hypertension [high blood pressure], tachycardia [rapid heartbeat], or hypocapnia [reduced carbon dioxide in the blood] relative to age-matched controls.

Design: Assess blood pressure, heart rate, respiratory rate, end tidal CO2 and visual analog scales for orthostatic symptoms when supine and when standing for 8 minutes without moving legs.

Setting: Referral practice and research center.

Participants: 60 women and 15 men with CFS and 36 women and 4 men serving as age matched controls with analyses confined to 62 patients and 35 controls showing either normal orthostatic testing or a physiological abnormal test.

Main outcome measures: Orthostatic tachycardia; orthostatic hypotension; orthostatic hypertension; orthostatic hypocapnia or combinations thereof.

Results:

n CFS patients had higher rates of abnormal tests than controls (53% vs 20%, p < .002), but rates of orthostatic tachycardia, orthostatic hypotension, and orthostatic hypertension did not differ significantly between patients and controls (11.3% vs 5.7%, 6.5% vs 2.9%, 19.4% vs 11.4%, respectively).

n In contrast, rates of orthostatic hypocapnia were significantly higher in CFS than in controls (20.6% vs 2.9%, p < .02). This CFS group reported significantly more feelings of illness and shortness of breath than either controls or CFS patients with normal physiological tests.

Conclusions: A substantial number of CFS patients have orthostatic intolerance in the form of orthostatic hypocapnia. This allows subgrouping of patients with CFS and thus reduces patient pool heterogeneity engendered by use of a clinical case definition.

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