Control of breathing in patients with short-term primary hypothyroidism.
In 8 patients (3 men and 5 women) with short-term primary hypothyroidism before and during replacement therapy, and in an age-matched control group (9 men and 7 women), we assessed maximal inspiratory muscle force (Pimax) and the ventilatory control system at neural (EMG), muscular (P0.1), and ventilatory (VE and Vt/Ti) levels. While hypothyroid, patients exhibited a significantly lower Pimax. During a CO2 rebreathing test, hypothyroid patients exhibited similar diaphragmatic electromyographic (EMGd) and ventilatory (VE) response slopes to increasing end-tidal CO2 tension (delta EMGd/delta Pet CO2 and delta VE/delta PetCO2), but significantly less delta P0.1/delta PetCO2 (p less than 0.05) and delta(Vt/Ti)/delta PetCO2 (p less than 0.05) response slopes. During replacement therapy with L-triiodothyronine (L-T3), Pimax (p less than 0.05), delta P0.1/delta PetCO2, and delta(Vt/Ti)/delta PetCO2 response slopes were found to be significantly increased (p less than 0.05 for both) while neither EMGd nor VE response changed significantly. We concluded that short-term hypothyroidism does not seem to be associated with blunted neural inspiratory output (EMGd), the respiratory control system seems to be affected mostly at a peripheral (muscular) level, and L-T3 increases both force (P0.1 and Pimax) and velocity (Vt/Ti) of inspiratory muscle contraction.
Gorini
M
M
Istituto di Clinica Medica III, Universita' degli Studi, Firenze, Italy.
Spinelli
A
A
Cangioli
C
C
Gigliotti
F
F
Duranti
R
R
Arcangeli
P
P
Scano
G
G
D000328:Adult; D003964:Diaphragm / Q000503:physiopathology; D004576:Electromyography; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy / Q000503:physiopathology*; D007320:Inspiratory Capacity; D008297:Male; D008875:Middle Aged; D012119:Respiration; D014284:Triiodothyronine / Q000627:therapeutic use*
D014284:Triiodothyronine