title: The role of cardiac sympathetic innervation and skin thermoreceptors on cardiac responses during heat stress.
abstract: The mechanism(s) for the changes in cardiac function during heat stress remain unknown. This study tested two unique hypotheses. First, sympathetic innervation to the heart is required for increases in cardiac systolic function during heat stress. This was accomplished by comparing responses during heat stress between paraplegics versus tetraplegics, with tetraplegics having reduced/absent cardiac sympathetic innervation. Second, stimulation of skin thermoreceptors contributes to cardiovascular adjustments that occur during heat stress in humans. This was accomplished by comparing responses during leg only heating between paraplegic versus able-bodied individuals. Nine healthy able-bodied, nine paraplegics, and eight tetraplegics participated in this study. Lower body (i.e., nonsensed area for para/tetraplegics) was heated until esophageal temperature had increased by ~1.0°C. Echocardiographic indexes of diastolic and systolic function were performed before and at the end of heat stress. The heat stress increased cardiac output in all groups, but the magnitude of this increase was attenuated in the tetraplegics relative to the able-bodied (1.3 ± 0.4 vs. 2.3 ± 1.0 l/min; P < 0.05). Diastolic function was maintained in all groups. Indexes of left atrial and ventricular systolic function were enhanced in the able-bodied, but did not change in tetraplegics, while these changes in paraplegics were attenuated relative to the able-bodied. These data suggest that the cardiac sympathetic innervation is required to achieve normal increases in cardiac systolic function during heat stress but not required to maintain diastolic function during this exposure. Second, elevated systolic function during heat stress primarily occurs as a result of increases in internal temperature, although stimulation of skin thermoreceptors may contribute.
authors: Department of Health Sciences, Nara Women's University, Kita-uoya Nishi-machi, Japan; shiba@cc.nara-wu.ac.jp.
authors: Manabu
authors: M
authors: Shibasaki
authors: Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine and Nachi-Katsuura Research Center of Sports Medicine and Balneology, Wakayama-shi, Japan; and.
authors: Yasunori
authors: Y
authors: Umemoto
authors: Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine and Nachi-Katsuura Research Center of Sports Medicine and Balneology, Wakayama-shi, Japan; and.
authors: Tokio
authors: T
authors: Kinoshita
authors: Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine and Nachi-Katsuura Research Center of Sports Medicine and Balneology, Wakayama-shi, Japan; and.
authors: Ken
authors: K
authors: Kouda
authors: Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine and Nachi-Katsuura Research Center of Sports Medicine and Balneology, Wakayama-shi, Japan; and.
authors: Tomoyuki
authors: T
authors: Ito
authors: Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine and Nachi-Katsuura Research Center of Sports Medicine and Balneology, Wakayama-shi, Japan; and.
authors: Takeshi
authors: T
authors: Nakamura
authors: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital and Department of Internal Medicine, University of Texas Southwestern Medical Center.
authors: Craig G
authors: CG
authors: Crandall
authors: Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine and Nachi-Katsuura Research Center of Sports Medicine and Balneology, Wakayama-shi, Japan; and.
authors: Fumihiro
authors: F
authors: Tajima
mesh_terms: D000328:Adult; D016275:Atrial Function; D001831:Body Temperature; D002302:Cardiac Output; D016022:Case-Control Studies; D006321:Heart / Q000294:innervation / Q000502:physiology*; D018869:Heat-Shock Response; D006801:Humans; D008297:Male; D008875:Middle Aged; D010264:Paraplegia / Q000503:physiopathology; D011782:Quadriplegia / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000502:physiology*; D013823:Thermoreceptors / Q000502:physiology*; D016276:Ventricular Function
keywords: cardiac systolic and diastolic function; hyperthermia; skin thermal receptors