TY - JOUR
T1 - Cerebrovascular and corticomotor function during progressive passive hyperthermia in humans
AU - Ross, E.Z.
AU - Cotter, J.D.
AU - Wilson, L.
AU - Lucas, S.J.E.
AU - Fan, J.L.
AU - Ainslie, P.N.
PY - 2012/3/1
Y1 - 2012/3/1
N2 - The present study examined the integrative effects of passive heating on cerebral perfusion and alterations in central motor drive. Eight participants underwent passive hyperthermia [0.5°C increments in core temperature (Tc) from normothermia (37 ± 0.3°C) to their limit of thermal tolerance (T-LIM; 39.0 ± 0.4°C)]. Blood flow velocity in the middle cerebral artery (CBFv) and respiratory responses were measured continuously. Arterial blood gases and blood pressure were obtained intermittently. At baseline and each Tc level, supramaximal femoral nerve stimulation and transcranial magnetic stimulation (TMS) were performed to assess neuromuscular and cortical function, respectively. At T-LIM, measures were (in a randomized order) also made during a period of breathing 5% CO2 gas to restore eucapnia (+5% CO2). Mean heating time was 179 ± 51 min, with each 0.5°C increment in Tc taking 40 ± 10 min. CBFv was reduced by ∼20% below baseline from +0.5°C until T-LIM. Maximal voluntary contraction (MVC) of the knee extensors was decreased at T-LIM (-9 ± 10%; P <0.05), and cortical voluntary activation (VA), assessed by TMS, was decreased at +1.5°C and T-LIM by 11 ± 8 and 22 ± 23%, respectively (P <0.05). Corticospinal excitability (measured as the EMG response produced by TMS) was unaltered. Reductions in cortical VA were related to changes in ventilation (V̇E; R2= 0.76; P <0.05) and partial pressure of end-tidal CO2 (PETCO2; R2= 0.63; P <0.05) and to changes in CBFv (R2= 0.61; P = 0.067). Interestingly, although CBFv was not fully restored, MVC and cortical VA were restored towards baseline values during inhalation of 5% CO2. These results indicate that descending voluntary drive becomes progressively impaired as Tc is increased, presumably due, in part, to reductions in CBFv and to hyperthermia-induced hyperventilation and subsequent hypocapnia.
AB - The present study examined the integrative effects of passive heating on cerebral perfusion and alterations in central motor drive. Eight participants underwent passive hyperthermia [0.5°C increments in core temperature (Tc) from normothermia (37 ± 0.3°C) to their limit of thermal tolerance (T-LIM; 39.0 ± 0.4°C)]. Blood flow velocity in the middle cerebral artery (CBFv) and respiratory responses were measured continuously. Arterial blood gases and blood pressure were obtained intermittently. At baseline and each Tc level, supramaximal femoral nerve stimulation and transcranial magnetic stimulation (TMS) were performed to assess neuromuscular and cortical function, respectively. At T-LIM, measures were (in a randomized order) also made during a period of breathing 5% CO2 gas to restore eucapnia (+5% CO2). Mean heating time was 179 ± 51 min, with each 0.5°C increment in Tc taking 40 ± 10 min. CBFv was reduced by ∼20% below baseline from +0.5°C until T-LIM. Maximal voluntary contraction (MVC) of the knee extensors was decreased at T-LIM (-9 ± 10%; P <0.05), and cortical voluntary activation (VA), assessed by TMS, was decreased at +1.5°C and T-LIM by 11 ± 8 and 22 ± 23%, respectively (P <0.05). Corticospinal excitability (measured as the EMG response produced by TMS) was unaltered. Reductions in cortical VA were related to changes in ventilation (V̇E; R2= 0.76; P <0.05) and partial pressure of end-tidal CO2 (PETCO2; R2= 0.63; P <0.05) and to changes in CBFv (R2= 0.61; P = 0.067). Interestingly, although CBFv was not fully restored, MVC and cortical VA were restored towards baseline values during inhalation of 5% CO2. These results indicate that descending voluntary drive becomes progressively impaired as Tc is increased, presumably due, in part, to reductions in CBFv and to hyperthermia-induced hyperventilation and subsequent hypocapnia.
UR - http://www.scopus.com/inward/record.url?partnerID=yv4JPVwI&eid=2-s2.0-84859615190&md5=c03022fa4ab93234291f62c3bdbc0464
U2 - 10.1152/japplphysiol.00988.2011
DO - 10.1152/japplphysiol.00988.2011
M3 - Article
AN - SCOPUS:84859615190
SN - 8750-7587
VL - 112
SP - 748
EP - 758
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 5
ER -