Author + information
- Michael F. O'Rourke, DSc∗ ( and )
- Michel E. Safar, MD
- ↵∗Suite 810, St Vincent's Clinic, 438 Victoria Street, Darlinghurst, Sydney, NSW 2010, Australia
We are concerned about methods used by our esteemed colleagues, Coutinho et al. (1), and question their conclusion, based on higher characteristic impedance (Zc) and lower total arterial compliance (TAC), that the aorta and large elastic arteries of women are stiffer than those of men. Both calculated Zc and TAC relate volume to pressure without scaling. The aorta of a child is small. With growth, Zc decreases and TAC increases, but this cannot be interpreted as lower stiffness because arteries become more, not less, stiff with age (2). Likewise, small animals have higher Zc and lower TAC than larger animals. Because there are systematic differences in weight and height between male and female adult cohorts (2), the (smaller) females will appear to have stiffer arteries (i.e., higher Zc and lower TAC) than men if not appropriately scaled for body size. When appropriately scaled to aortic cross-sectional area in Table 1 of Coutinho et al. (1), Zc in males (172 × 10 cm2 = 1,720 dynes · s · cm−3) and in females (211 × 8.3 = 1,751 dynes · s · cm−3) are virtually identical. With the same scaling, TAC also appears identical.
Scaling is used elsewhere in the authors’ data analysis, but not consistently. Smaller echo dimensions in females are consistent with smaller body size (Table 1 ). Height and weight are not provided in the table, text, or online appendix.
The authors’ Table 1 (1) contains many anomalies that ought be considered and explained. Amplification of the pressure wave between the central and peripheral sites is 3%, not 5%, in males, and −3%, not zero, in females. Both values are much lower than measured invasively (2). Mean pressure, calculated as (brachial diastolic blood pressure × 2 + systolic blood pressure) ÷ 3 (data supplement ), is 93, not 97, mm Hg for males and 92, not 98, mm Hg for females. Values for left ventricular (LV) outflow tract diameter must be centimeters, not millimeters (i.e., 2.3 cm male, 2.0 cm female). Taper in diameter of 55% in males (35.6/23.0) and 63% for females (32.6/20.0) over a length of <5 cm between the LV outflow tract and site of aortic diameter measurement (which we do not challenge) must create secondary flow and turbulence in the aorta (2). There is concern also on the low value of pressure amplification compared with those in the authors’ reference 9 (1) and in the paper by Safar et al. (3) in the same issue of the Journal.
The authors are highly respected clinical investigators and colleagues, and may not be aware of the aforementioned anomalies, if their data were analyzed in an outside center without adequate technical scrutiny. We have not been able to trace the source of the quoted “NIHem” on the Internet. We need stress in papers such as this, Carl Ludwig’s dictum: “Die Methode ist Alles” (2).
Differences in arterial hemodynamics between adult males and females do exist, but can be attributed to shorter body length with earlier return of wave reflection, and hence, greater aortic pressure augmentation in females (the authors’ Table 1). Such greater pressure augmentation accounts for impaired LV relaxation and the higher prevalence of diastolic heart failure in females (2). In this, we certainly agree.
Please note: Prof. O’Rourke is the Founding Director of AtCor Medical and significant shareholder.
- American College of Cardiology Foundation
- Coutinho T.,
- Borlaug B.A.,
- Pellikka P.A.,
- Turner S.T.,
- Kullo I.J.
- Nichols W.W.,
- O’Rourke M.F.,
- Vlachopoulos C.
- Safar M.E.,
- Balkau B.,
- Lange C.,
- et al.