It is well known that the cardiopulmonary system is crucial for the delivery of oxygen to various bodily tissues as well as for the removal of metabolic waste. In addition, the cardiopulmonary system has a vital role in regulating bodily temperature, as well as assisting in the transport of various hormones and nutrients to bodily tissues. Whole blood is a two-phase suspension, consisting of plasma (liquid phase) and numerous cellular components (solid phase); given that erythrocytes are the primary cellular component, the unique mechanical properties of blood can be explained by the characteristics of red blood cells (RBC). RBC tend to form three-dimensional microstructures (rouleaux) when under low shear conditions. The rate and magnitude of RBC aggregation can be quantified using photometric methods, which measures the amount of light passing through a blood sample for a discrete time period. The quantification of specific aspects of RBC aggregation, such as the extent of the aggregation, the time course of aggregation, and the magnitude of the aggregating forces, has been shown to be important from a clinical perspective. Analysis of the RBC aggregation process provides valuable information, which can be utilised to determine the presence of various adverse health conditions (e.g., sepsis, diabetes mellitus and myocardial ischemia). Therefore, RBC aggregation analysis – as a possible health indicator – may play a crucial role in the clinical management in several patient groups. The Laser-Assisted Optical Rotational Cell Analyser (LORCA®) and the Myrenne® aggregometer are photometric instruments commercially available for quantifying RBC aggregation. Disadvantages of these systems include elevated cost and lack of portability (i.e., size, weight, power consumption). The Myrenne aggregometer is possibly the most extensively adopted hemorheological analyser; however, the absence of a temperature control and the inability to provide information about the time course of RBC aggregation, represents a significant disadvantage in regards to experimental research. In this context, a new instrument which is designed to overcome the major limitations of current commercial aggregometers may have an important impact in the health care domain. Low cost, portability, low-power consumption, computer independency, and built-in graphic interface are the cardinal features of a newly-developed instrument described in the present thesis. Furthermore, the portable capillary tube RBC aggregometer (PCA) is able to analyse the aggregation time course and provide relevant parameters. The design of the PCA facilitates an intuitive way to control its operation through the various phases of the aggregation process. Moreover, the PCA’s integrated graphic interface allows the user to visualise the aggregation curve in real time during the data collection process. The engineering process of the present device was conceived as the result of the latent need to bring low-cost specialised equipment to remote regions where budget, transportation facilities and/or power supply restrictions are major limitations for use of current technologies. Blood samples from 43 individuals were analysed to compare the results yielded by the new newly-developed aggregometer, those produced by a commercial device, and the measurements obtained using the erythrocyte sedimentation rate (ESR) technique. The results obtained with the new PCA showed an enhanced signal quality evidenced by a superior signal-to-noise ratio when compared to that yielded by the Myrenne aggregometer. In addition, the precision assessed for the PCA from the aggregation index at 120 seconds (AI120) and aggregation half-time (T ½) measurements reflected a good reliability of the instrument. Furthermore, a strong correlation between PCA and the Myrenne aggregometer for the AI120 parameter was found. An unexpected finding allowed this study to hypothesise that the PCA may be able to predict ESR measurements due to the sedimentation phenomenon observed on the blood sample contained in the capillary tube. Unusual aggregation curves were obtained as a result of the RBC reorganisation being detected by the PCA’s infrared sensor. Based on these results, it was possible to obtain the linear equations to predict the ESR in a fraction of the time required for the traditional practice (i.e., Westergren method). Moreover, the possibility to predict ESR by using a small blood sample (~50 μl) at a fraction of the current required time (i.e., 5 min) will expand the PCA’s applicability in a wide range of scenarios. The significance of this study is represented by the overall performance of the PCA as a modern medical tool. Given that the newly constructed PCA accurately determines various RBC aggregation parameters, it may be suitable for use as a regular screening tool, and assist in the early detection of particular diseases. Importantly, utilising the newly constructed PCA device at point-of-care (i.e., health care facilities) would promote the use of preventative medicine.