Hypoventilation is considered a complication of hypothyroidism. In this study we tried to evaluate the changes in ventilation through measurements of endtidal PCO2 (Et-Co2) occurring in patients with mild(subclinical) and severe(overt) thyroid hormone deficiency compared to healthy controls.
We investigated 33 subjects with subclinical hypothyroidism (TSH 4.5 to 19.99αIU), 31 with overt hypothyroidism(TSH > 20 μIU) and 31 healthy control subjects. All subjects were females and three groups were age mached. All subjects were evaluated clinically by an endocrinologist for evidence of thyroid disease and catecorized clinically also. TSH and fT4 levels were measured using radioimunometric assay. EtCo2 was measured using Ordion Microstream Capnograph. Mean values of three measurements was considered EtCo2 value of the individual. Student t-test was used for test of differences and pearson test used to test correlation. P < 0.05 was considered statistically significant.
Mean EtCo2 values of subclinical hypothyroid group was significantly lower than healthy controls(31.79 ± 2.75 versus 33.81 ± 2.38; p = 0.012). This value was also lower in overt hypothyroid group compared to control group(32.13 ± 3.07; p = 0.048 ). Also there was no significant correlation between FT4 and TSH levels and EtCo2 in these 95 subjects of three groups tested (r = 0.11; p = 0.28, r = −0.126; p = 0.22 respectively).
These results indicates that the minute ventilation as can be inferred from EtCo2 level is higher (lower EtCo2) in subjects with subclinical hypothyroidism and overt hypothyroidism compared to healthy controls and no meaningful relationship exists between EtCO2 and the level of TSH or FT4 levels.
Patients with thyroid hormone deficiency have acually higher rather than lower minute ventilation in a stable state.
Khalil Ansarin, No Financial Disclosure Information; No Product/Research Disclosure Information