STUDY DESIGN, SETTING, SUBJECTS AND PATIENTS We performed a prospective observational study in healthy male volunteers during experimental endotoxemia induced by 2 different dosing regimens, and an observational study in sepsis patients. Data were obtained from a total of 19 healthy, non-smoking, male volunteers, aged 18 to 35 years, 11 of whom were included in a human endotoxemia study employing continuous infusion of LPS, and 8 of whom were included in a human endotoxemia study employing single bolus administration of LPS. All subjects provided written informed consent and experiments were in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines, and approved by the local ethics committee Commissie Mensgebonden Onderwoek region ArnhemNijmegen with document numbers NL57410.091.16 and NL53411.091.15 on 29 August 2016 and 6 January 2016, respectively. Project identification codes are: Clinicaltrials.gov NCT02922673 for continuous infusion of LPS; Clinicaltrials.gov NCT02675868 for single bolus administration of LPS. Subjects were screened prior to inclusion, and had a normal physical examination, electrocardiography and routine laboratory values. Also, 10 patients with septic shock, older than 18 years, were included. The local Institutional Review Board waived the need for informed consent for these sepsis patients. Septic shock was defined by the international sepsis definition conference . Sepsis patients were treated according to international management guidelines . All sepsis patients received sedating medication and were mechanically ventilated to achieve normocapnia. Exclusion criteria were an irregular heart rhythm or an insufficient transtemporal bone window. EXPERIMENTAL HUMAN ENDOTOXEMIA Purified LPS (continuous infusion study: _Escherichia coli_ O:113, Lot no. 94332B4, List Biological Laboratories, Campbell, USA; bolus administration study: US Standard Reference Endotoxin _Escherichia coli_ O:113, Pharmaceutical Development Section of the National Institutes of Health, Bethesda, USA) was supplied as a lyophilized powder and dissolved in normal saline 0.9% as described previously [23,24]. For the continuous infusion study (c-LPS), a total of 4 ng/kg LPS was administered as a intravenous loading bolus of 1 ng/kg body weight at T = 0, followed by an intravenous infusion of 1 ng/kg/h for a period of 3 h . For the bolus administration study (b-LPS), LPS was administered, as described previously, as an intravenous bolus injection at a dose of 2 ng/kg body weight in 1 min at T = 0 .